google "apps2sd", i have a feeling froyo adds this ability anyway, so you might want to google that and check, if so you might want to wait for froyo (only 1-2 weeks away)
If you want a good mod while you wait for froyo install "voodoo" (lagfix only package) for galaxy s, very easy to install and uninstall makes the phone a beast. Also if you root the phone install "autokiller" if not rooted then install "advanced task killer" Both extremely easy to install, basically put update.zip on the sd card, boot into recovery mode and choose "update" there is an update.zip for voodoo and an update.zip for rooting and unrooting. to uninstall voodoo you just create an empty file then when you reboot it automatically undoes the lagfix.
There is no point in flashing firmwares as it's much more complicated and Froyo firmware is around the corner anyway.