Many rewards credit cards come with sign-up bonuses. If you are after such one-time offers, then keep in mind the following. Not everyone is eligible for a sign-up bonus, so make sure you can get it before you apply. Also, sign-up offers come with specific requirements which you should fulfill to qualify. That is usually spending requirements so check them out as well.
And finally, it takes time to get your bonus once you qualify (6-8 weeks on average). If you are planning a trip and want to pay for your airline tickets or a hotel room using that bonus, make sure it will post to your rewards account on time.