I just ordered one of these:
SUMVISION SV-K053 WIRELESS KEYBOARD with BUILT-IN TOUCH PAD
Not bad for £20. Since the Pi will be in a lounge plugged into a 42" LCD it seemed right to go wireless with a device you can easily perch on your lap. A separate mouse would be a pain under those circumstances.
For power I propose to use a Kindle USB charger as I have a spare, and I also have a very cheap (£1.99) HDMI cable. I'm not yet sure about the SD card, I have a few lying around but most are too small. All advice taken on that one!
I think the problem is how to kit up without it costing a fortune. I mean, in the spirit of the R-Pi's low price, I am trying to keep everything else low price too (subject to certain extravagances like the keyboard for the reason stated).