Recumbents come in a couple of different varieties, some 2 wheel and some 3 wheel.
2 wheel versions are SWB or short wheel base, and about the same length as most BMX or mt bikes. These are usually about as high as regular bike (aka wedgie or diamond frame in bent speak). The pedals on these stick out above the front wheel and are usually a bit higher than your butt.
LWB or long wheel base are longer framed. On these bikes, your feet are lower than the frame, sit behind the front wheel and you generally ride in a more upright position.
There is also a CLWB - compact long wheel base - typically a bit shorter than a standard LWB.
Then there are a whole host of other styles - high racer, low racer, and more. Plus different handle bar styles - OSS, or over seat steering, which is like the handle bars on a regular bike, - and USS or under seat steering, which is typically found on LWB's and the handle bar sits under the rider's seat. Very fun to steer!
3 wheel trike versions come in 2 basic styles - tadpole, where the front is 2 wheel with 1 back wheel - and delta, which is where the front is 1 wheel and the back 2 wheels, like a traditional trike.
Trikes are extremely fun to ride!
This is what my bike looks like - it's considered a CLWB, generally, though there is some debate in bent community.