Don't know much about the 550D to be honest but I'll tell you the reasons I went with a 60D anyway & that may help in your decision...the 550D probably shares a lot of these qualities too, make sure you do your homework on it.
-the lens. 18-135 is a huge range for a walk around lens. On a APS-C crop sensor about 28mm is what the human eye sees, so 18 is a good wide angle shot and 135 zooms 5 times closer to the subject than your eye. (Note that this isn't the same as the 2x or 5x or whatever ratings that point & shoot cameras give. Those can be misleading & confusing if you ask me). If you get an 18-55 you have no telephoto for all intents & purposes, it zooms from a wide angle to slightly closer than your eye. Not much range IMO.
-The swivel screen. While I don't use it often and live view is a joke for anything other than roughly framing up your shot, it's super handy when I'm trying to get pictures of cars from extreme high or low angles to swing that screen out & put it at an angle I can see easily. Also, when working on a tripod with weird angles I've found it useful to dial in the manual settings referencing the quick menu on that screen instead of contorting myself to look through the viewfinder.
-5.3fps continuous shooting - if you like action shots, being able to shoot a bunch of 'em & throw away the bad ones is nice.
-The body. Fits my hands REALLY well. The smaller DSLRs like the rebels & most nikons I've looked at just feel too cramped & the controls aren't where I personally would expect 'em to be. For the 60D it's all right there for my left thumb & laid out right where my hand wants to be. Good balance to it also. I can't remember if it's magnesium or some other kind of metal or what but it's a ton more beefy and substantial than a rebel body...it's a step towards professional grade cameras like the 5D & the build quality is really evident. And as a happy accident that I didn't plan on at all (and wouldn't really recommend basing a purchase decision on), while shooting for fun at 2 car shows I got hired by people to photograph their cars for 'em based solely on "I was looking for someone who looked professional & noticed your camera." Between those 2 gigs and 2 referrals I got from their friends that liked the shots...my 60D was free.