I'm stuck with 2.1 (HTC Desire) for the time-being, so the APP2SD provided by Froyo isn't available to me.
I use Appbrain which allows you to keep a synchroised list of the apps installed on your phone in your own (free) online account - and then the Appbrain app on the phone will then automatically allow you to reinstall the apps you had before. I've used it numerous times when re-flashing my ROM.
Downside - it's a fresh install; so you lose any data within the apps. Upside - free, easy and takes the ball-ache out of reinstalling; it also allows you to install apps on the phone directly from the appbrain site.