I have used the CT-Art program (a little) and it looks impressive.
It can be used for building up pattern recognition by testing by themes, or by testing your general ability by testing random puzzles by rating.
The slight feedback is a little helpful in comparison to using a book as gives you a second chance - and feel you learn better if find for yourself rather than looking up answers in a book.

They also do a Strategies program that I'm interested in but haven't seen.
There is also a ChessCafe CD by Kartsen Muller that is strategy based (the 2nd Volume I think), but again haven't seen it for myself - but is another I'm interested in. I'm assuming it's similare to the books that came out.

- Tickly

I like a lot the Convekta programs: CT-Art for combinational vision, Chess Endgame Training for endgames and I've found Mate Studies useful to become more methotical and accurate when calculating variations.