AVG is good but it does have a limit of one install per household so be careful that with a home network - you can't run it on more than one machine. For that reason I switched to Avira, seems to be just as good, allows multiple copies.
The latest version of Ad-aware seems a bit intrusive so I switched over to SUPERAntispyware Free Edition, seems to work just as good. Free version doesn't support scheduling but it is easy to use.
Also a Spybot user. I'd recommend it for a beginner.