Prices for 80 Gig harddrives vary between 70 and 120€ overhere. You can never have too much discspace imo, since games are becoming larger and larger as well. If you play a lot of games, and like to keep em on your harddrive for a longer time, i'd go with the 80 Gig one.
I just saw an add for a 250 Gig harddrive, but that's a little over the top if you ask me. When you wanna scan that one, you might just as well go on a short vacation. By the time you get back, it's probably finished.