I had a lot of positive reactions on the piston monorail, so i decided to make an improvement! This one goes in two directions, just build one train and go back and forth as much as you like!
This one is a bit more trikcy to build, so definitely read these notes first!

*BUILDING IT
This schematic contains 4 parts, 2 edge sections, and 2 mid sections that you can copy as much as you like. Make sure all the parts are leveled and flush! you should get one straight block in the end.

*USING IT
Place a normal and sticky piston facing toward eachother, put about five blocks behind those, and then put another sticky and normal piston, vica versa. The train can in theory take off anywhere on the track, but this may not always work properly. Also do not build much more or less than 5 blocks in between the pistons.

Additional Notes

Also check out the 3.0 version: http://www.planetminecraft.com/project/piston-monorail-30/