Instead of a 5D, I suggest considering the 7D with the EF-S 17-55mm f/2.8 IS. It's the only standard zoom with both IS and 2.8.
Better to put the money into glass rather than the small improvement from 7D to 5D.

Check the box -- I think you mean to say the Rebel T2i.

It ain't the 550D unless it came from overseas (highly unlikely with Best Buy).

Of course, I have been using the name interchangeably. My bad.

That's a solid path. Personally, I think the best reason to get the 5D2 is if you want to use fast primes. You can't really get anything faster than f/2.8 in a wide lens on the 7D. On the 5D2, you can choose from the EF 28/1.8, EF 24/1.4, Zeiss ZE 28/2 or others to cover the wide end in dark conditions.

Like you say, it's all about the glass. And the glass you choose really depends on your shooting goals.

The other side of the coin is that many lens have vignetting and soft corners on 5D but they will look fine on 7D because it is crop and so you have more to choose, it will not look good on 5D but perfectly fine on 7D, I think it is best to have both full frame and crop.

Short story is this: if you need wide angle, you're better off with the EOS 5D Mk. II.

When I answered I was thinking about saving money. I was also thinking that I don't like the kit lenses on the 7D or 550. I think the 17-55 on the 7D and 550d and the 24-105 on the 5D are the best choices for most people. For a $2000 budget the 550 with the 17-55 would be my choice.
If someone is buying a set of fast Canon or Zeiss primes the camera body cost difference is probably not important. But I do agree that some people try to save money on the smaller APS-C sensor, but then end up buying an additional lens to cover the wide end. It takes some planning.
As far as vignetting or softness in the corners of the 5DII, I just don't see that as a problem. Especially with video.

On the 5D, you can get the EF 28/1.8, EF 50/1.4, and EF 85/1.8 for about $1k used. They're not L-glass or Zeiss, but they'll all look better than an f/2.8 lens when the light is low. That's the equivalent of a 17.5, 31, and 53mm lens on the 7D. They don't have IS, like the 17-55 zoom, but they are 1.3 to 2 stops faster.

Or you can spend $10k on three Zeiss CP.2 lenses. :)

But at that point, I might look at a PL conversion on a 7D. Then one could rent an Ultra Prime as wide as 12mm at T1.9, or a Master Prime as wide as 14mm at T1.3. Though if I had that budget, I'd look at a ONE if not 35mm film.

But I digress...