Are you looking for novelty such as skillers, prayer pures, or something to actually play on like a PKer?
Skiller wise; Skiller are fun if you have the time, and definitely not hard to make if you just go for the easy 99's first.
Pkers; Summoning tanks are very fun, however obviously it requires membership, and is really time consuming to make. If you don't want to put a lot of work into it, your best of just doing a simple pure, range/obby /claws /chaotic something along the lines of that.