Couldn't find a post like this so, I'll try to start one.

Frequently (I do these monthly, depending on usage):
  Error Check (right click on drive, properties tools  "Check Now" check both boxes and restart machine)

  CCleaner  (3rd party freeware application http://www.ccleaner.com/) Clean

  CCleaner  (3rd party freeware application http://www.ccleaner.com/) Issues (repeat{scan and fix} until 0 issues found)

  SFC /scannow (start run "sfc /scannow) (info can be found on this site System File Checker - An XP Maintenance Utility? http://www.fixmyxp.com/content/view/35/129/

  Spybot search and destroy (3rd party application from safer-networking.org) (update, immunize and search for spy ware)

  Defragment  (right click on drive, properties tools "Defragment Now"


  Create a restore point

I also weekly
  Check patches from Micro$oft
  make sure my virus definitions are current (I'm set to daily get updated)
 

Alright people, is this an adequate list?  I know some prefer other products to spybot S&D, and CCleaner.... am I missing something important?