Most people finish the game with a character level in the range of mid forties to low fifties. There is no specific level cap, but without cheating or running into a bug, it would be very difficult to get much above level 53. The experience points (E) required to reach a particular level (L) is given by the formula below (for example, level 50 requires 4,165,000 experience points).
E = 1000*(L^3 - L)/3
see also:
Wisdom - is it worth the skill points?
