If you go with Corsair, go with LL, not C2. The price isn't much more, and there were problems reported with C2 when nForce2 was first released.
If you go with Corsair XMS PC2700, get TwinX LL for less.
Kingston HyperX PC3000 should do at least the Corsair rated timings at PC2700, but costs significantly less.
If you want something in the middle, you can check out the Twinmos PC3200 that use the same Winbond 5ns chips that Corsair does. I don't have a link to a reputable dealer, but you should be able to turn something up in hot deals or in CPU/OC'ing if you can't find a link in a search in this forum.
Also, don't feel like you're stuck with Newegg. I've found Googlegear to consistently be the price leader of reputable online e-tailers, and I bought my XMS TwinX 1024LL from Monarch a few months ago b/c Newegg was charging $40 more for it!!! Use Googlegear as a reference point and then do some comparison shopping.
Faster RAM is always good when it comes to future compatibility/OC'ing, but personally I think you're limiting yourself a bit by buying 2 x 256MB now. I guess it really depends on what you plan to use your PC for and when you think you might need more RAM, but I've felt that going with 1 x 512MB and getting a second later is the better move. Also, as they say, that last 10% in performance always costs the most, and the same is true for memory. I don't think anyone will argue that Corsair is the best when it comes to doing their rated speed at a rated timing, but expect to pay for it. I've gone through enough RAM and found that tha the flexibility of excellent RAM when it comes to OC'ing was worth the extra money.
Chiz