Assorted tools that I've found useful when working on puzzle hunts.
ariados is a tool suite that provides a simple anagram checker, pokemon lookup, and a code sheet.
phenomist's Sets of Things is a list of sets of things that show up frequently in puzzle hunts.
enigmatics.org brute force checker for checking strings against a bunch of different encryption algorithms.
Mystery Hunt Word Search to run regexes against various dictionaries. You can also use Nutrimatic and Qat for similar tasks.
MIT Mystery Hunt Puzzle Index: All Keywords to check out similar puzzles from the past.
betaveros’s Have You Tried? to get unstuck.
dCode to decipher coded messages.
Sudoku Solver to solve sudoku puzzles.
MIT Mystery Hunt Puzzle Tools & How-To's