Now that you have a handle on strategy, try endgames or tactics (whichever you consider to be weaker). Better yet, split your time and work on both so as to avoid boredom.
Originally posted by Jusuh Chessmaster 8000/9000/10K would be good choice. Or Fritz...
ChessMaster is good for the lessons by Waitzkin and Seirawan, but for post-game analysis, it's terrible. Fritz, since you mentioned it, is *much* better.
Tactics and endgame study are critical to chess development. Pick one, or both, like Zebano said.
Get a copy of The Ultimate Chess Puzzle Book by John Emms and go through 5-10 of the puzzles from the first 3 chapters each day. Don't worry about the harder puzzles until you have these down pat.