You can check out different sites' rake structures on a page i made some time ago. This is for LIMIT holdem, and for the case where you are not getting a discount because of few players at the table.
http://www.aalborgmob.dk/rake.php
For NL games I think all the sites do it the same, or at least there is not much difference. They take rake in 1c or 5c increments amounting to 5% of the pot, up to 3$