I will compare HP to UA and AA. I'm sure someone else can give the specs on other airlines.

HP:
B757 - 14 seats
B737 - 08 seats
A319 - 12 seats
A320 - 12 seats

AA:
B757 - 22 seats
B738 - 16 seats
B762 - 9 F seats and 30 J seats
B763 - 30 J seats ( two class cabin)
B777 - 16 F suites and 35 J seats (Atlantic config)
B777 - 18 F seats and 35 J seats (Pacific config)
MD80 - 14-16 seats depending on reconfig schedule
A300 - 16 F seats

UA:
B733 - 8 F seats
B735 - 8 F seats
B747 - 14 F suites and 73 J seats
B752 - 24 seats
B762 - 10 F and 33 J (NA config 1)
B762 - 10 F and 32 J (NA config 2)
B763 - 34 F
B763 - 10 F and 32 J (Intl config)
B772 - 36 F (NA config)
B772 - 12 F and 49 J (Intl config 1)
B772 - 10 F 45 J (Intl config 2)
A319 - 8 F seats
A320 - 12 F seats