Windows Classic
I don't use any of the visual effects or Aero options other than those that work while in Windows Classic mode. I.E. Aero Snap. It might only give you a marginal performance enhancement, but personally I don't really care if my computer is all shiny and pretty.
To enable Classic Mode w/ no visual effects:
Right Click Computer > Properties > Advanced System Settings > System > Performance Box > Settings Button > Adjust for Best Performance