If you're thinking of bonuses and that sort of thing, I would advise checking out all associated costs with the broker first. A lot of the time, they advertise them to get you to look away from other unfavorable terms. A $30 welcome bonus isn't really worth anything if you're trading with a broker that charges high spreads or ridiculous withdrawal fees, for example. Not saying it's always a bad thing, just that you should be mindful of that and don't choose a broker *just* because they have bonuses.
Honestly, a lot of the better brokers don't have bonuses, but they give you the best prices. Those that do give them aren't going to give you anything for free, so you can guarantee they are going to make that money back somehow.