Thus far I've made use of AV (by far my favorite part of the software suite), Speed disk, Norton Diagnostics (helped me identify one of my RAM sticks as being defunct), System Information (great when you have programs running in task manager but can't quite figure out what they are from the name alone), and a few of the registry/program trackers (though this always seems to somehow end up in an error, and so I've avoided it as of late).
I got mine as a birthday present back in Jan. of 2000, and would say that the first two programs mentioned above (anti-virus and speed disk) make the entire package worth it. You could get AV by itself if you'd like, though when the entire system works costs only around $10 more, it's not going to set you back a great deal to splurge.