On a 7D I've done the 400x or 533x cards - and yes, you'll notice the speed difference compared to the 30MB cards if you're doing high speed continuous shooting.
Lots of options on cards, make sure you get 'authentic' ones though if going for SanDisk or other top brands. I've used ADATA and Transend without issues on Canon cameras.
Interesting about Transend. I've seen a lot of them about on the internet, but their prices have always made me wonder what was wrong, or maybe just different about them for them to be that much cheaper.
Without knowing which camera you have, its hard to give the best advice. If your camera supports UDMA7, for example, that's a good choice. Otherwise, its a waste of money.
I suggest that you tell us which camera you have.
I have a 7D
I'll be ordering a larger, faster card later this month I think. Just wish everything I want/need wasn't all coming at the same time, becoming an expensive time of year!