I highly recommend the Chess Tactics Server (CTS). I've been using it since last week whenever I have a few spare minutes. The great thing about it is the rating system and the running clock--motivational tools that aren't there when you're just looking at diagrams and trying to solve them.
I don't get into time pressure very often these days, but I think that this practice would also help in finding the right moves in those circumstances, as well. With the demand to solve the easier problems on CTS within 6-10 seconds comes a useful concentration on the important points in the position.