Are there any others?
Chesstempo.com is the one I use. It's pretty excellent. I'd like to hear if there's a better one, though.
Free: 5 problems/day
chessity.com is fun, and the free membership offers 20 puzzles/day and access to multiplayer games.
chess24.com 5 free problems a day.
Lichess.org has both tactics and opening training.
Take a look at this.This chessbase site is pretty useful.