I've heard there are tons of affiliate networks in the casino field, but which is the best one if you are still starting out and haven't really established your site that much yet?
I don't find them to be that profitable but they do have good support, there are a bunch of reputable programs. I would advise you to visit AGD, they have descriptions of each program and who to avoid and why, useful resource
It really depends on what countries will you target. If you target European players i would advise 888, Europartners, Affiliates United (William hill).
You could try some inhouse affiliate programs from some of the well known sites, or even some of the major affiliate networks have some casino related offers