
- Probability and Random Processes by Grimmett
- Probability with Martingales by David Williams
Grimmett is probably a better bet to start with since it doesn't expect quite as much prior math knowledge and covers a lot more topics. The Williams book is shorter, denser and doesn't cover much in the way of applications, but gives a really good theoretical underpinning of how probability theorists think about probability (ie in terms of Lebesgue measures and Sigma algebras).
edit: There is also a companion book to Probability and Random Processes called One Thousand Exercises in Probability which contains an interesting selections of problems and solutions that will let you apply the theories taught in the main book.
However, in probability thing can quickly get complicated and, for me at least, intuition can't always be trusted. (I probably needed to go to the lectures and read the book.) For examples see either Schwarz's 40 Puzzles and Problems in Probability and Mathematical Statistics or Grimmett and Stirzaker's larger One Thousand Exercises in Probability.