When buying a computer, big drops in prices are always right around the corner, so if you live by that philosophy, you're never going to get a new PC.

As far as graphics cards go, yes, I would wait before buying one now, for the 8800GTX to come down in price.
I wouldn't buy two GPUs and use SLI; I couldn't justify that when one card would suffice. Granted, sometimes two cards are cheaper than one, but in that case you're not going to get the same power as one card.
Basically, with GPUs, you get what you pay for.

500W PSUs won't generate more heat unless you're using the whole 500W. If you're using 380W from your 500W PSU, it'll generate as much heat as a 380W supply. Note, however, that PSUs don't generate anywhere near as much heat as a CPU or GPU.

A card reader sits in the front of your PC like a floppy drive,, but instead of 3.5"s it takes flash cards. So if you have an SD card or an MMC card, or a CompactFlash card, etc. you can plug it in and transfer files directly. This is a <i>major</i> (we're talking 1000%) speed advantage over software used to transfer files through a device onto the card.