Ok thanks a lot everyone!
I was looking on eBay and saw Transcend cards 16GB for 28€ or something, they had 133x 'speed', but from this thread I'm starting to think that isn't enough.
And how does speed affect taking photo's in burst mode? Shooting burst on a 5DmkII on the highest settings, you'd probably need more than 133x speed I reckon? But how is this with the 20D? Of course I don't want to get the minimal standard, I'm trying to think long term here, bear with me: Let's say I want to upgrade to another camera (with video! 1080p/30fps and 720p/60fps) in a year or I don't know when, what would be the minimal writing speed I'd need on those highest settings (if I'd get the 550D I would need an SD of course)? I know people with a 550D shooting video always say they need class 10 stuff because otherwise they can't shoot well. How does this go with compact flash? What does class 10 mean and what would be the maximum writing speed of that?
I think I'll probably go with some 400x (60mbs) I reckon that would be enough, good quality and what not. The only thing I'm worried about is if it would be able to hold up when shooting in HD Video?
EDIT: I just saw that the xxD line went from using CF to SD storage. The 50D used CF still, but the new 60D uses SD's. Now, is this something that's gonna happen with all camera's now? Is the 7D mkII gonna have SD instead of CF? Or are there advantages from CF over SD?