the rule (?) is 1 virus scanner, 1 firewall - and as meny malware scanners as you can be bothered with
virus
AVG, AVAST, AVIRA are free - I pay for kaspersky
if you are buying - the suite is the best option - everything is integrated and works together.
firewall
komodo, zone alarm - both free
spybot search and destroy, malware bytes, ad-aware - all free
there are others - but be careful
CCleaner will keep your system clean of rubbish (once a month or so)
finally defrag 2 or 3 times a year
all free - and better