1. Non-deposit bonus to try the site (if it is NEW)
2. If it is Old sites, they should give reward to their loyal player.
3. Jackpot for Nice Hand like 4 of a kind, straight flush, Royal Flush etc.
4. Free rolls is a must.
Most of these already exist on the site.
One thing I like and see only on one site is the use of Krills.
Just like pokerstars offers player classes, we need something like that for the BTC poker community as well.