It gets better in gen IV and V. Stockpile boosts your def and spdef each time you use it, so you've got +3 on both defenses (150% boost, iirc).
Besides Smeargle, there are no normal type pokemon who can learn Spit Up, so its power is always 300, except when against resistant mons, where it's 150 (still a decent strength move).
My favourite (and perhaps overused combo) is a Scizor with a Focus Band, U-Turn and Technician.
Technician = 1.5x boost in power for moves under 60 power inclusive. U-Turn is power 60, it goes to 90 power, plus STAB bonus putting it at 135 power. Choice Band = +50% attack boost but allows only one move to be selected. Nine resistances and only one weakness. A perfect Scizor with a Choice Band on can reach 591 Attack, along with its buffed Technician U-Turn allowing it to both scout and hit hard, while resetting the choice band penalty. Think about metagaming like that for a second.
Good defenses. Middling speed. Lots of resistances. A great ability. Scouting moves. Item that boosts attack. And the fact that Psychic and Grass tend to be pretty darn common, and Scizor becomes an insanely hard hitter.
I'll break it down.
U-Turn = 60 base.
Technician U-Turn = 90 base.
Technician STAB U-Turn = 135 base.
Technician STAB 2x (super effective, as in Psychic or Grass) U-Turn = 270 base.
Technician STAB U-Turn against Exeggutor or Celebi = 540 base power.
Technician STAB U-Turn against Exeggutor or Celebi + Choice Band boosting attack by 50% = the equivalent of 270 + 540 = 810 power.
AND THAT IS JUST FOR A NORMALLY WEAK ESCAPE MOVE.