Primedice is probably one of the best gambling sites out there for bitcoin users, the games are all provably fair with 100% transparency, being able to check each game with its own seed and code, the ability to change your own client seed which believe it or not does affect your chances and can reduce the likelihood of hitting the house edge which is at a low 1%.

I had 0.008 on the site and in the space of maybe four or five hours of careful and sometimes risky betting I have managed to get to 0.098 which is almost 0.1 of an increase in only a short amount of time, check out the site it is well worth the time and bitcoin :)