There's also a DC 35 tumble check to stand as a free action (forget if you still provoke an AoO or not) in Complete Adventurer.
There's also my favorite option, the 600 gp boots of agile leaping, from magic item compendium, which allow you to stand from prone as a swift action without an AoO if you have 5 ranks in balance. THe boots also let you use dex instead of str on jump checks, and are totally worth even paying +50% to tack onto another pair of boots or paying x2 for a non-body slot.
There are two skill tricks that let you stand from prone as a swift or immediate action (one skill trick for each) that require tumble ranks to get. Skil tricks are in Complete Scoundrel.
Barring ALL of that...yeah, tripping's great against medium/small humanoids. Anything that's bigger, has many legs, huge str/dex, flying, etc...? Not so much. Just throw a greater variety of enemy types at the party, so trip only dominates some of the time. Heck, you can't even do it on creatures more than one size larger than you. And if there's not a great chance of success, failure could lead to the PC on his back. In my group, people don't usually bother with tripping unless they have a fairly good advantage on the opposed check (or they stop trying once they realize they don't have one).