An OC 8800GT and a 1GB 8800GT sit at around the same price level. The one to buy is really going to come down to personal preference. I'm not a huge fan of large amounts of memory on cards that aren't at the very top of the high-end scale. Really, what the extra memory gives you is a bit of bragging rights, but most of the time if you're talking to somebody who knows their tech they will know that you're simply paying more for no real benefit.
What the ASUS 8800GT 1GB does offer over the overclocked card here today is an extra 12 months warranty, an aftermarket cooler that does a better job of keeping the core cool along with a funky little CD Wallet.
Performance on the card is of course good, it performs like an 8800GT should, but it doesn't offer the increase that you might think it will.
Fortunately, with the other bits and pieces that ASUS has strapped on to the card make the justification for buying the 1GB 8800GT from them not too difficult. You're getting a better quality cooler, and there's no denying that more memory isn't going to hurt you. Of course, you could then fire up something like Rivatuner and start messing around with the clock speeds.