Sklansky Bux Calculator
PokerTracker - Records every single hand you play and every dollar you earn. Features many player statistics and the ability to playback hands for later review. PokerTracker is necessary for the use of Pokerace HUD. Costs $55.
PokerAce HUD - a Heads Up Display that uses PokerTracker to display playing statistics of your opponents in real-time while you play. Legal to use on all poker sites that support PokerTracker. Costs $35.
PokerStove - With user input, calculates how much equity one hand or hand range had against another. Useful for any tournament or no-limit cash game player.
Full Tilt Table Mods - Excellent site for free table mods. The link will take you directly to full tilt's section, but you can get mods for any site by changing the "site browsed" on the left hand side.
Full Tilt Shortcuts - A must have for any serious Full Tilt player. It does everything from bet sizing, to auto clicking the time bank button. There's a free 1 table trial, so check it out, I gurantee you won't be disappointed. $25 sign up fee, then $12.50 a year.
Real Time HUD - The future replacement of PAHUD. 100% free, has 3 bet stats, works on all major sites and many minor sites like Cake Poker! There really is no reason to ever buy PAHUD again.