With 7. I will add to this as I find / try them, so far:
Ccleaner (works fine, no issues)
JK Defrag (as above) Since the built in defrag in 7 is just as bad as the one in Vista (I've asked about this so will let everyone know what they have to say) I think they may have given up since so many third party defrag programmes are better and faster.
Have been looking at what seems to me to be a novel Firewall solution. Vista Firewall Control is a small application which integrates with the Windows 7 firewall to give control over outbound traffic without having to configure that part of the Windows firewall. It seems to work quite well and is very simple to use. It detects any software attempting outbound traffic and presents four options. Allow once. Allways allow . Deny once. Allways deny. And it's free. click here
I use Outpost with XP but they don't have a version ready for the beta - yet.
Nero Essentials v7.0 loads(but if you allow it to update then it removes the old version and doesn't install the update!) Not tried burning a disc yet though. LightScribe function with Nero didn't install but LightScribe software based on HP did.
CoffeCup Free FTP v4.0
Avery Design Pro Lite V5.0
Whisper 32 (surprising as this little password wallet application was written for Win 95!)
Also tried MS Money 2000 and MS Frontpage 2000 and both seem to work fine.
So far only had problems with a webcam and with a networked all-in-one from HP. Printer installs fine but Vista driver/software doesn't work so still trying to sort out scanning functions. May be simpler if it was USB connected but, hey, where is the challenge in that!
Macrium reflect - click here - is disk imaging software similar to Acronis TI and the free version works with Windows 7. Being free, it's slightly less well featured than the commercial version, but it fulfills it's main function very well and, being free, it's a bit of a bargain.