This is the one that I have seen most everyone use:
CombatStats
Some other options:
ParseMania
StatAnalyzer
I am not sure about the others, as I use CombatStats, however the "posting" of Stats is as simple as making sure the fight has ended, hitting return, using cntrl-v (the paste command), and then hitting enter again. Building this into a UI as a bottom is fine but shy away from any Parser that pastes this information automatically after a fight. The developers, in response to a inquirer by the creator of CombatStats, have specifically said that ANY 3rd party program that is automated to send information to the EQ2 client will be considered a violation of the TOS.