New build :) ready to mod

I've had a fun friday evening building a brand new system

EVGA e-Geforce 8800GTX
Intel E6550 core 2
Creative X-Fi Elite Pro
Apevia X-Cruiser case
Asus P5K-E motherboard
2x1gb cheapo Kingston, 500gb hdd, Pioneer DVDRW

This machine cost me £650.

Actually I have a second 8800GTX, unfortunately I got most of these parts at bargain price and was rushed on choosing the motherboard; the P5K-E supports CrossFire not SLI... d'oh!

I've never been bothered about modding before but since this system is so nice, and so blue and glowing... I feel I should do a bit more. My previous system was a P4 2.8 with nvidia 5700 so this is a fairly big step up.

In a month or two I'll be getting an SLI motherboard and some decent RAM, and possibly a faster CPU, moving the spare parts to another case for a work computer. In the mean time I'm thinking about water cooling and other possible mods for when I'm running SLI, I have a feeling it's going to get HOT...

So basically, any tips and suggestions for a newcomer?

(Incidentally I closely missed out on landing an EVGA Black Pearl mobo + 8800s for a ridiculous price. I'm trying to forget all about that though...)