If you like to bet sports, you can get a free $25 Free Play to bet on sports here: youbetonit.eu
Really that is FREE?
-SNIP-
Try BitStarz! They will give you a registration proof of 180 free spins and spend it all away by losing!
Just kidding though, Fortunejack.com is said to be the largest gambling site where you would be able to win 1BTC with a high rate of winning it. They will give you 25 spins once you have successfully registered as a new user so enjoy your gaming and good luck.