Types of Intermediate Representations

As I've researched on the Internet about compilers, I've run across a few different types of Intermediate Representations, including plain AST's, Single-Static Assignment, Continuation-Passing Style, and others. Sometimes, it's hard to tell what each type is good for.

If you implemented a compiler (or another piece of software with an IR), what type of IR did you use and why? What did you like about it, and what annoyed you?