We've seen airlines like Virgin Atlantic and Air New Zealand test their biofuels on existing engines, but that's not going to be the best long term solution. The key is finding ways to become even more efficient. There are a couple of efforts going on to achieve this goal.
First, we've seen Pratt & Whitney break out the Geared Turbo Fan (GTF) concept. In fact, the engine has just finished ground tests, and they're preparing for flight tests soon.
These engines seem great in theory, because the gears allow the different stages to run at optimal speeds whereas now they all have to run at the same speed. According to the company, that will lead to a 12 percent reduction in fuel consumption, 50 percent reduction in noise, and significant emissions reductions as well. The real key here, however, is finding out how it will perform over time. Past attempts have failed miserably because they couldn't get them to be reliable enough. This is quite a complex piece of machinery, so hopefully P&W has found a way to make it work.
Rolls Royce, meanwhile, has apparently dusted off the old open rotor idea. It effectively looks like a jet engine with the blades on the outside. This was all the rage back in the 80s and early 90s for its fuel efficiency, but there was a problem. Open rotors are loud as hell.
With the passage of time and the rise in oil prices, apparently manufacturers think they may be able to make it work this time. GE and SNECMA are getting together again (they make the CFM engines that power 737s together) to take a swing at the open rotor concept as well.
If any of these end up working, there are some significant fuel savings ahead for airlines. As long as fuel prices stay this high, engine manufacturers will keep working around the clock the get a next generation engine out there.