The bubble-tip anemone is probably the most popular option to host your clowns. They're readily available, can be very pretty, and are not difficult.
Just a quick warning about BTAs though. They can be a pain in the butt. They are mobile, and will climb all over the rock you place them on, until they find the spot they like, even if it's right on top of another coral, or in a spot you can't see. If you decide to go this route, I would recommend placing it on its own island. Grab a piece (or pieces) of rock and separate them from the rest of your rock work. The nems will crawl all over the rock, but won't cross sand. This will limit where they can go, and make it easier for you to manipulate their positioning. Be careful, because they can stretch pretty far, climb over rubble or glass.