All the bonuses I've seen are shit.
So far I've seen a few but the first that comes to mind is the PocketDice.io THAT usually auto activates itself when you have a new account.
Just look at this example.
https://bitcointalk.org/index.php?topic=1459229.msg14738866#msg14738866"
So i deposited first time on pocketdice my 1 mbtc
it goes up to 2mbtc (cause of bonus)
i was thinking "ok i depoisted accidently 2 mbtc"
so i gambled up to 50 or 60 mbtc i want withdraw
and i cnat...
talked on chat and i realized that there is bonus
1. You get double your deposit on 1st deposit
2. You need to gamble 700x that what u deposited
3. If not you ll loose your all winnings and go back to your deposit amount
...
i was so much happy that i did that amount but then i goes like suicde cause i tried gamble my last (10 mbtc) on other site and lost
and goes back to pocketdice for my 50 mbtc and that...
i lost it cause i needed that so fast and that happend...
be careful playing on pocketdice ;c im bust cause of this"
Nothing is free. Bonuses make you lose more than you win, and in the rare case you do win, it'll probably be marked as invalid.