1)defrag - not needed unless you have a habit of filling the HD to 95% or more , and even then there is no real need to do it
2)disk clean up - setup a cron job to empty some log files , but this is auto done about every 30 days on most distros of *nix. Every now and then you might want the thumbnail folder cleaned out .
3) check disk - see above post #2
4) various spyware removal - there is no spyware that runs on *nix -- not needed
5)virus scanners -- there are about 6 viruses that run on nix , and as far as i know non of them will install unless you run as root , and do something very dumb .
rootkits those can be a problem ,but only VERY rarely - install chkrootkit-0.48 and rkhunter-1.3.4