As has been mentioned any supposedly silver bullet here is unlikely purely due to the inability to make it in big enough quantity/volume fast enough. Instead a stream of many small silver bullets is required to simultaneously increase efficiency and move demand away from Oil/fossil fuels. Of particular importance would be suitable storage methods.
An awful lot of power generators sit idle at times, but still consuming resources, having a means to store this slack in the system would be very beneficial. The same technologies could be applied to patchy energy sources like wind, solar and tidal. If we could store a portion of their generated power from peak output it would be available later when direct generated supplies are low. At the moment there are few small scale solutions for this besides having large banks of relatively inefficient batteries. At the social scale large potential energy storage means are possible. Multi thousand ton flywheels have potential to store power but are limited in the amount and are major engineering feats of their own, with major energy investments. An uphill pumping system for hydro is an obvious solution, as is seperating reactive chemicals for later reaction to generate power, even generating hydrogen from water has potential to store currently wasted power. The problem with all these is scaling, cost and efficiency. The smaller the scale the better, the greater the efficiency the better and obviously the cheaper the better. I believe pumped water has nearly a 50% reclaim rate from energy applied if engineered right so maybe we need a lot more closed cycle dams constructed for storage purposes. These combined with a wind farm could lead to said farm producing a much smoother feed of power to the overall system and cover gaps in generation.
For generation of power, there are many smaller scale approaches that could supply a lot more power in smaller piecemeal bits to the grid, seperate they have only small effects, but many small effects become a large effect. Waste biomass from mills (wood and cane come immediately to mind), specifically grown biomass, thermal layer generation ( both high saline pond and ocean thermal ), Off shore current generation, Tidal, Wind, Solar (be it panel, exposed thermocouple, heat trap, tower*, closed cycle vertical evaporation**, tethered lighter than air***), large scale physical movement****. While a number of these are fanciful some are doable at least in small scale in many places across large areas of the planet. The key thing to remember is a lot of things have been shown to be better than break even over as little as five years but the scale of their generation and their generation curves are not as profitable as fossil fuel approaches at the moment.
For transport, efficiency should be king and it won't be unless costs go up, but as this post is about replacements I give you - Ethanol from sugar ( preferably from the most efficient source possible, probably tropic cane. ) is a suitable supplement to Oil based fuel and can either be blended or used as a complete replacement. Methane can be used and generated in many ways, biogeneration from biowaste products is certainly possible and we in the west do not lack biowaste. I believe there are massive problems with Factory production of Pigs etc and their waste, some farmers already use methane for heating purposes. Wood gas and Coal gas used to light the streets of London and New York and this gas could be used to power cars as well, the waste is barely waste either and can be used in other methods to generate electricity.
Now the problem with these approaches for both large corporations and Government is simply that they don't like dealing with large numbers of customers or suppliers and especially hate it when people are both. What is needed is a true means of financially reconpensing suppliers and users. If a user was charged the true cost, not given special deals by local and state governments conservation would occur. ( Here in Aus Governments have waved bills for Aluminium smelters to get them to locate here and then been forced to continue doing so to keep the company, In Queensland this currently eats nearly 1/8th of the power generated in the state. Many Government organisation waste huge amounts of power as well, I laugh/cry when I see well lit signs suggesting the conservation of power at 3 in the morning.)
On the supplier side forcing marketting boards to accept generated power and pay for it, even for small distributed generators would see a lot of additional insentive to generate power at small local scales. Excess power can be stored physically at a reduced payment to the supplier if they are over supplied. The problem with this is that it takes political will to reform energy distribution on both sides of the ledger and is resisted by what is easily the largest industrial sector in any country.
My number one technology though for massive energy reform would have to be efficient, compact, high density, energy storage. This would act as a moderator to power generation and as a boost to the use of electricity for auto use.
Just a few ideas.
Now for the asterisks, please ignore if you don't like overengineered small scale power generation ( or substitution ) methods
* Tower - Generates power from different means, heat lift from huge greenhouses and Wind sheer (a tower of 100 meters hight will almost always experience a wind sheer between its top and its bottom causing a draft to flow upwards).
** Closed cycle evaporation - Not exactly high power, but It can be used to shift water vertically. Evaporated moisture lifts to the top of a heating chamber and is then condensed into a higher chamber. Used by myself to purify water and get it 3 meters up a pole using little more than black plastic, the sun some plastic pipe, shade and a metal condenser. This can be easily boosted by the use of high saline solutions for heat trapping and reflected sunlight. I have seen a farm not far from where I live use five big black distilling tanks to evaporation lift water into two elevated tanks for small scale irrigation purposes. Apply additional solar heating and High saline fluid in the bottom tanks and a few micro hydro devices and the said hippy/biker/farmer could grow his crop off grid, with 24 hour lighting
. In Tropical climates this could easily generate power to at least assist low energy life, the tanks will be necessary anyway for localised water supply, just never drink from the black tanks. This can probably be done using other fluids and gas combinations but water is probably the easiest to use and least toxic.
*** Tethered lighter than air - Very interesting actually, Take one baloon, balute, blimp, zepplin. Paint it black to absorb heat as much as possible make it barely capable of lifting itself and several hundred feet of tether at the coolest point of the night. Wait for the sun. ( little known fact most zepplins had to carry ballast and excess gas to allow for moderation of elevation due to day night temperature variations even after they painted them with highly heat reflective materials. (The hindenburgs outer skin was actually highly heat reflective but also burnt very well.)) Now as the sun begins to warm the gas in the tethered baloon it proceeds to increase it's lift, apply massive gearing to this continuous vertical force and use the power to either generate power or refill vertical water storage. Large baloons can exert multiple 100's of ton's of vertical force continuously and will continue to do so for 8-10 hours of every day. Once cooling begins start winding the baloon in as gravity slowly returns it to it's next day starting position.
Alternative to the above, is to use said baloon to generate poweror use energy from drag in high wind conditions the only trouble here is the ability to retrieve the baloon. Some plans seem to use these types of baloons to apply force directly at times to transport in certain know wind corridors. This is done in similar ways to the sails of yesteryear, large surface area would cause a lot of wind assistance to something moving in the same direction. Tethered baloons apparently were capable of apply substantial force to ships during WW2 and cut fuel useage on West East Journeys, I imagine proper scheduling and courses would allow for substantial fuel savings during long Water passages.
**** Here in Aus, and I assume in other countries, We have a large number of Trains (5000 + tons) carrying large volumes of produce and minerals from multiple 100 meter elevations to sea level. Often a lot of the journey is actually flat and only in relatively short distances is most of the elevation traversed. Regenerative breaking transfering power into the grid during these descents would have to assist generation as a whole, but being short term peak generation would be best at refilling local energy stores. Train schedules should easily allow vertical water stores to be refilled for later use in local power generation.