[ponokareefer]

I had tried anemones in my old 33 gallon, and if you have corals in there, there is a very good chance they will get stung. Just a word of warning. Ken had some very good points though. They vary a lot. Depending on your lighting, you may want to look at a long tenacle anemone or a sebae anemone, as they both stay on the bottom, and less chance of wandering onto corals that are high up on rocks, and will typically stay away from powerheads in a smaller system as they don't usually go up the rock work/glass. This isn't always the case though.
Bubble tip anemones are typically known as the easiest to keep anemone, but they like to be up in the rock work, and can move around much more than the previous 2 I mentioned.
Another thing to consider if you do get one, you probably don't want it growing really fast in that size of tank, so you will want to limit any type of food it gets, and just let it catch what falls to it, rather than spot feeding the anemone.
What type of lights do you have on the system, do you have sand on the bottom of your tank, what do you have in your tank right now and how long has your system been running?