The 550D T2i, as most other dSLRs in it's price range, is a very well-balanced Camera that can do a bit of everything well.
If you're looking into video, currently it's the only option good enough for professionals you'll find anywhere near that price. It's better than the 1000-1500$ camcorders, and it's in the same league as the 7D and the 5DmkII. The 5D has a bigger sensor, but an older software, so depending what you're filming, it's either the 5D or the 7D/T2i that will come out on top.
When it comes to photos, though, what makes a camera good or not in low-light, sports, portraits, etc, is the lenses you'll buy with it. A 800$ camera with a 2000$ lens will take better photos than a 2500$ camera with a 300$ lens.
I very strongly recommend a 50mm f/1.8 at 99$ on top of the kit lens (18-55mm IS), and a good telephoto lens (the 55-250mm IS seems very decent and is affordable, a 70-200mm would be better if you have the budget for it).
Like agun says, though, you might want to wait after photokina to see if the newer Nikon cameras will also have 1080p. If they can reach 1080p, improve their video quality a bit, and take their insanely amazing ISO noise reduction they have on their top model and put it in their lower models, then Nikon might be leading the video side for a while also. For extreme low-light (i.e. one candle lighting up a whole set), the top Nikon camera is already leading, but in any other scenario, Canon makes better videos.
In either case, though, the Canon T2i would at least still be good enough for professionals, so even if Nikon releases a better one in a few months, I don't think us T2i owners will feel the need to regret our purchase.
Cameras: Canon EOS Rebel T2i, Canon S90
Lenses: Tamron: SP70-300mm F/4-5.6 Di VC USD, Canon: EF-S 18-55mm f/3.5-5.6 IS Lens, 75-300mm f/4.0-5.6 III, and EF 50mm f/1.8 II
Retired camera: Fujifilm Finepix s700