MicrostockGroup

I use the Extreme 3s and 4s, and they work just fine.

I've been using Extreme III 4GB cards for the most part.  I like the smaller cards for most things so I don't risk losing everything with one faulty card.  Plus the older smaller cards can be pretty affordable.

Great advice.  I've hesitantly gone up to 8gb, but it takes forever to dump onto my portable drive.

I use both Extreme III and Kingston 133x, mainly 8GB, and I can't tell the difference between them from my 1Ds MkIII (no video though obviously). Don't forget the primary limiting factor on capturing images is the speed and capacity of the camera's own buffer, not the speed of the card itself.

Even 8GB cards have a huge capacity __ nearly twice that of a standard 4.7GB DVD for example. You normally get more memory for your money with the smaller card sizes.

I always like to check out this page
http://www.robgalbraith.com/bins/camera_multi_page.asp?cid=6007-9784

a ton of cards ranked and rated for the 5D mark II (or any other camera if you select it)
then I buy a card that I feel is a good compromise between $$ and speed.

I am currently using Sandisk 16gb Extreme III and have been happy

266x is doing just fine, and I use 32 GB

I'm in the smaller is better camp - I have Extreme IVs, 8GB. I use my older cards too, and for most purposes those seem fine too.

Whatever you decide do not buy Lexar they didn't work in my 5D Mk2 (and a lot of other Canon models apparently), I use Sandisk and have never had a problem.

D5-II: Sandisk 32GB Xtreme III. If you go higher in size or speed, you'll pay a hefty price. I like to keep my cards under 100 euro since I don't like the early adopter's premium. There are faster and larger cards all the time. In 2002 I bought a 256MB card for 100 euro. 64GB is too much for now. I can shoot 3 days with it. Sure, they can break down, but every spare moment I save the new shots on my laptop.

I had bad experiences with Kingston (both USB sticks and cards). Perhaps the ones they sell in the West passed a better QC but the ones you buy in the East get fried after a while. I never had any problems with all my Sandisks.

If you count on doing a lot of video, try the Xtreme IV. My III gave some glitches. Perhaps that's due to the fact I work in the tropics in an ambient temperature of 35°C+.

Thank you for the advice, I checked the site store I'm gonna go tomorrow and that's what they have:
 
SanDisk Extreme IV CF 16 GB 16GB @ 45MB/s - 169€

Versus

SanDisk Extreme III CF 16 GB 16GB @ 30MB/s - 69€

* it, it's a huge difference... I wonder if it is worth it considering I have to buy 2 of'em

Yep I heard of that and probably makes me go for 2 the Extreme IV, wow it will be a nice punch in the stomach 

hmmm yes it's way too much and it's obviously overpriced