For Windows XP users, the built-in firewall should be enough (or prove me otherwise, those who know better?) wheeras for antivirus, spam filtering and spyware protection, I use and recommend AVG Free (free AND auto-updating, every few hours sometimes!) and Spybot-Search & Destroy (free, not-auto-updating, but hey, do something yourself occasionally, eh?)
(hide) Keep your Inbox clean by Archiving important messages and regularly using the Delete All Messages in your Inbox option. (pauloaguia) (show all tips)