Enhancement software? What like cleaners? I'll just list individual programs that I use to prevent ads, spyware etc. Their in order of my fave to least fave, not necessarily most crucial otherwise Virus Scanner would be top.
1. Adblock (Firefox plug in to block ANY ad/ad source!)
2. Firefox
3. Tweaknow Reg Cleaner
4. Ad-awre
= Spybot
6. Panda Online Active Scanner - If I think my regular virus scanner has missed something I use this website (it can only be used with IE though)
7. McAfee Antivirus as I get it on a free licence, otherwise I'd use Avast
8. Windows Firewall - I have a hardware firewall so this is just a little extra security, on it's own, Windows Firewall is not sufficient
I'm looking forward to seeing how much IE7 improves the line. They have to add better features, improve security and comply more with the W3C guidlines and it shouldn't be hard for Microsoft to do this now they finally have a competitor to sit up and take notice of (Firefox). My friend asked me if I had downloadedf the IE7 Beta as he had, my response was "final release Microsoft products are buggy enough".