As you download programs, you should periodically be using
Menu | Settings | Manage Applications and selecting those programs and "Move to SD card". Not all programs automatically move themselves to the SD card.
I prefer using a download from the Market called Free Advanced Task Manager for the purpose of moving programs rather than the Menu | Settings and Manage Applications method, because in one view, I can check multiple programs and move them to the SD card more effectively. I can also clearly see what is installed on the Phone, and what is installed on the SD card easily with this tool. Moving things to the SD card makes it possible to load the phone with more games, apps, tools.
When you manage apps in this way, you have another button available "Clear Cache". You can individually select each program and one at a time Clear Cache.
However, a better tool for clearing all the caches at one time IMHO is a download called 1Tap Cleaner.
Last but not least, sometimes, Froyo launches a bit too many programs at the same time and phone behavior may become flakey. I have downloaded Advanced Task Killer Free from the Market. I run this maybe once a day.
A good alternative to manually killing everything is physically shutting down the phone every couple of days, thus doing a reboot.
Everyone tells you that Android and specifically Froyo does a very good job of memory management this is true to some extent, much better than the predecessor OS version called Eclair. My experience with both the Samsung Intercept and the Motorola Triumph is that while it may be better, it's not perfect.
I have had a good experience using these tools periodically to keeping the performance of the MT up to expectations.