There are a few good choices.. NOD32 is definitely the best if you've got some money to spend in my opinion.. Free choices include (and are certainly not limited to) Avast! (works extremely well with Win 7, there is also a paid version if you'd prefer), AVG Free (It works, somewhat... can't really say much else than that about AVG, as it pretty much sucks... Kaspersky is also one of the better one's..
The free versions of PCTools for firewall, antivirus and something called Threatfire install okay on Win7 .... too soon to tell if they do what they are supposed to do. But no problem in 6 weeks so far. Anyone else using them? Threatfire is supposed to be both antispyware and antivirus.