I have recently had 2 Lexar 4GB 80x cards go bad on me after only 1 year of use. I don't want to run the risk of having a bad card while on my safari, so it is time to replace the Lexar with something else.
The Sandisk Extreme III 4GB cards have just come down in price to $239.95 (from over $400 not more than 1 month ago). That's a great deal for a high speed 4GB card - matches nicely with the high performance capabilities of a Canon EOS 1D MK II N
If high speed is not critical to you (not shooting to many 8 fps bursts), then you could get the Sandisk Ultra II for $179.95, or even the Sandisk 4 GB Compaq Flash Card for $149.95.