If you want nice round figures, I can offer you this approximation:
- O: 45%
- A: 40%
- B: 10%
- AB: 5%
But if each ABO group is divided into a rhesus +ve and -ve component, the pretty figures get quite messed up. It is always far more common in the general population to be rhesus +ve than -ve. In white people, around 15% are -ve, whereas in native black and asian people (as opposed to those living in, say, America, where some sexual mixing between the races has occurred), it is extremely rare to be rhesus negative (<0.3%).
The above figures can vary significantly depending on which country is measured. For a look at the figures for several 'common' countries, you can go to a Wikipedia page here.