I like Sandisk cards as I've got plenty and have never had a card fail. I use a Sandisk Extreme Pro 90mb/s compact flash cards in my 5D Mark II.

However the 550D uses SD cards, for video I would recommend Sandisk Extreme Pro SDHC/SDXC 95mb/s card. Capacity is your choice but I'd go for either 16gb or 32gb.