Free download: holdemcalc.exe
This software computes the odds of Texas Hold'em Poker. Simply enter your hand in the left hand pane, and it will tell you your average chances of winning and making certain hands.
It can also be used in live games to calculate desired pot-odds, however this does not take into consideration the way other players are betting. In that case, it's better to enter hands using the keyboard (e.g. type "K TAB H TAB 6 TAB S TAB" for King of Hearts, Ace of Spades).
It estimates the odds by generating 5000 random decks and counting the outcomes.