There are keyframes for filters, track motion, pan/crop....envelope points are technically keyframes, what are you after?
right click a keyframe and you can change its attributes as well.
"What" filters are, is what some people call Plug ins. Same thing, basically. Another name for them is "Video FX" or video effects. Sometimes they're called proc's.
BTW, there are also keyframes for transitions, too. There are two excellent articles on keyframes in Vegas on the VASST site if you'd like to check those out.