Much of the energy used in an aircraft is for keeping it up in the air.

It is an attractive idea to use helium or hydrogen to do the lift, and only use energy to move the aircraft through the air. However with a lighter than air craft, there is a lot more aircraft to move through the air, so more energy wasted on air resistance.

As usual, a compromise.

Human powered blimp

White dwarf is a human powered blimp.

Bill Watson's elegant White Dwarf established new records with the FAI when Bryan Allen pedaled it for 58 miles in 1985. This feat and the craft's remarkable design earned it the cover of the Smithsonian's prestigious magazine Air & Space.

http://www.solar-flight.com/whitedwarf/index.html

Aeroscraft  ML866

The Aeroscraft model ML866 is a planned 20-ton hybrid airship, to be built by the Worldwide Aeros Corporation.
A scaled-down prototype was made in 2008. However, development of the first Aeroscraft is still underway.
The sheer size of the aircraft will make them comparable to luxury liners with room aplenty for passenger staterooms, bars, restaurants and other amenities currently offered on ocean-going cruise vessels.

It will be able to take off vertically and fly similar to a plane by using the small wings. Most of the lift is provided by the helium inside. Inside it will have 5000 square feet of space. Cargo will go in teh centre and and passengers around teh outside. It will be capable of flying 155mph.

Wikipedia

Aeros Pelicanto Airship 

The Worldwide Aeros Corp has developed Control of Static Heaviness, or COSH. As the airship needs to descend, it compresses helium rather than venting it to the atmosphere.

This new zeppelin airship is being developed for the U.S. Department of Defense. The best thing about this new air vehicle is that it is a mixture of an airship and airplane with the function of carrying cargo across long distances and not having to take off from or land on a runway as it lands and takes off vertically, and can also remain on the ground when being loaded without the need for tethers. The only disadvantage about the Pelican is lower speed that that of a standard airplane. The earliest test flights for the Pelican have been scheduled for early 2013.  

It is funded by the Pentagon’s Rapid Reaction Technology Office. Source

Update from Aeroscraft 2012

The multilayer composite outer cover has been applied to 85% of the vehicle.

We are determined to finish the vehicle before the end of 2012.

The Aeroscraft is a rigid, ballast- less air vehicle with true VTOL at the maximum payload of 66 tons with no infrastructure requirements,  At 1/3 of fuel consumption, it has the ability to operate at low speed, in hover, from unprepared surfaces, and off-load with minimum ground handling.  Source 

Helium or helium?

Hydrogen is easy to make but helium is rare. There is a small percentage in the atmosphere, but commercially it is extracted from natural gas. Underground uranium gives off alpha particles in spontaneous radioactive decay. Alpha particles are helium nuclei and as soon as they pick up a couple of electrons, each becomes a helium atom.

Unfortunately the US sold most of their helium so it has become rarer.

Still on the drawing board?

A wonderful old idea to set the imagination going.

It was solar powered!

Hindenburg

The Hindenburg used hydrogen for buoyancy. It was made with an aluminium frame covered with painted cotton. Inside the hydrogen was held in 16 gelatin coated bags or gas cells. 

Between the bags were large vents running from bottom to top.

It caught fire and was destroyed. Current thinking is that on landing some hydrogen leaked out of one of the bags and was rising up through the vents. Unfortunately the blimp was landing in a rain storm. Ropes had been dropped to the rain sodden ground and earthed the frame. The tail fin was seen giving off an electrical discharge (St Elmo's fire) and this set light to the hydrogen escaping out the vent.