Hi Andrew,
My son has the 1000D (which I use for astrophotos which cant do video and only 10MP) and also a 550D now.
Notable differences are the 550D is 18MP compared to the 1100D (12MP) and the 550D can do HD video (1080p) compared to the 1100D (720p)
Check out here (no affiliation with me)
http://www.digitalcamerawarehouse.co...FY-FpAodBH_Ong
as the price difference between the two with a stock 18-55 IS lens is only $60!!!!!
Go the 550D, for sure
Cheers
Chris