Puzzle Buffs International - Featuring books on crosswords as well as online crossword puzzles and word search games. Puzzle Master - Computer generated puzzles. Puzzle People - Human produced not comper based. Standard, cryptic, clueless and trivia crosswords. The Puzzlemakers Site - Puzzles at all levels of difficulty.
Site provides samples.
Scientific Crosswords - A collection of free to download scientific crosswords. Search Lessons Learned from Crossword Puzzles - Abstract paper by Matthew L. Ginsberg. Tidbits Puzzles - Features selection of short and small crossword puzzles. Cafe - Each puzzle has two sets of clues to choose from. USA Today Crosswords - Crosswords from USA Today.