First, I have and use the 20/2.8 a lot. It's an excellent lens and I like it on both full frame and crop sensor cameras....Harbor at Morro Bay. Canon EF 20mm f2.8 lens at f5.6, with B+W Kaesemann C-Pol. EOS 50D camera at ISO 200, 1/400 shutter speed. Handheld.
Internet resolutions don't do the above image justice. There is far more detail than you can see in a reasonable size at 100ppi. When I was printing this image I thought at first I'd shot it with my 5DII... Was a little surprised to see it was shot with one of my 50Ds. That's thanks to the quality of the 20mm lens.
But, it does closely duplicate the focal length of your 18-55mm kit lens. I bet the 20mm is better corrected and I know it's a much better built lens, though.
If you want to expand your focal lengths, I'd suggest you consider an ultra wide zoom such as the Tokina 12-24, which would cost about the same as the 20mm. It's a very good lens and "L-like" in build. The Canon 10-22 is another excellent ultra wide, perhaps a little more flare resistant than the Tokina, but costs about $300 more than the Tokina or the 20mm.
Another tack you could take, if you wanted to start shooting with a prime instead of zooms, you might consider a 50/1.4. This Canon would cost about $100 less than the 20mm and makes for an excellent portrait lens on a crop sensor camera like your 50D. There is also a Sigma 50/1.4, which a lot of people like but it is more expensive than the Canon. A somewhat wider option would be the Canon 28/1.8 or Sigma 30/1.4. These two are close to a "normal" lens on a crop sensor camera.... A normal lens approximates the angle of view of the human eye. A longer lens for tighter portraits, perhaps more candid, would be the Canon 85/1.8. It costs about the same as the 20mm, last time I looked. Note that all these lenses enjoy larger max apertures, and will be better at throwing the background out of focus and/or usable in lower light than the 20/2.8 or the zooms you already have.
I prefer primes, but I also keep a set of zooms for times when they're necessary. This doesn't mean you have to like shooting with primes, though. A lot of folks only use zooms, which are fine for many purposes.