Elder-Basilisk
First Post
Brother MacLaren said:50/50 isn't bad against a larger opponent; use your lower iterative attacks for Trip. They aren't as likely to hit normally (especially if you're Power Attacking), but you only need a touch attack to make the trip attempt.
50/50 with improved trip means something like a 50% chance of success, a 30% chance of backfiring (since the Imp Trip +4 doesn't apply to opposing a foe's trip attempt), and a 20% chance of doing nothing. It will sometimes be a good idea, but isn't a good idea in general--even with iterative attacks.
Ring of Spell Storing with Righteous Might would still enlarge you, wouldn't it? You wouldn't be totally self-contained, but unlike the polymorph approach your ability scores would remain (but adjusted).
Not much that I know of boosts the offensive side of Trip attempts; there's the feat, size, and Str. This is probably a good thing.
There are a number of other ways to boost tripping potential: prayer, enervation, ray of exaustion, waves of fatigue/exhaustion, and ray of enfeeblement all spring to mind.