For paid software I've been recommending Kaspersky, Norton AV/Internet Security is a worthy option also, for free anti-virus the 2011 version of AVG is an excellent choice, I've moved away from recommending MSE as there are too many bad reports surfacing against its effectiveness. All-in-one suites such as Norton 360 and Kaspersky Pure put too much in one package which can cause performance issues and unexpected problems for end-users.