aboyd
Explorer
StreamOfTheSky outlined many ways to avoid the problems with tripping, and some of them are very good and legitimate. So don't be afraid to look them up and use them.
And don't forget other things too, such as dwarves being more difficult to trip, four-legged creatures being impossible or super-difficult to trip, distance attacks, escape mechanisms such as the "panic button" from Complete Scoundrel, etc.
For example, anyone tripped can escape with any number of spells. In fact, this happened in a game my friend Sam ran a few weeks ago. I was playing an Abrupt Jaunt wizard (free 10' teleport as an immediate action). I also had the 1st-level spell Benign Transposition. When an ally was down and surrounded, I cast the spell to swap places, and then teleported away. If my PC can do it, the bad guys certainly ought to be able to do it.
(Technically, there are two ways to rule on how Benign Transposition works. You can say that the two characters swapping places are literally swapped right down to position of limbs -- the prone guy ends up standing where the wizard stood, and the wizard ends up lying on the ground where the prone guy fell. In that case, you need a second "thing" you can do to get the wizard away from the bad guys, such as the Abrupt Jaunt teleport feature I mentioned. However, most DMs seem to rule that Benign Transposition works like this: the spell simply swaps squares -- so the prone guy ends up where the wizard was, but still prone, and the wizard ends up where the prone guy was, but still standing. If you rule that way, then that spell alone is good enough to save a prone NPC. The downed character will disappear and reappear wherever the wizard was, still prone but not surrounded. And the wizard will appear in the surrounded position, but he will not be prone so no worries about AOO. Knight's Move is a similar spell that requires the character to teleport into a square that would flank a bad guy, but it doesn't require any characters to swap places. Also, it's a swift action spell, which means the fallen character can cast it on the ground without provoking attacks of opportunity, and then instantly transport away from the crowd. He would still be prone upon arriving at his new location, and he'd be next to a bad guy, but one bad guy is better than 5.)
Other spells like the darkness and mist spells will help. Swift Invisibility from the Spell Compendium would allow a character to turn invisible (swift spells do NOT provoke AOO, so it's safe to cast it), and once invisible the bad guy could crawl away or stand without provoking any attacks. Another swift spell, Lightfoot, blocks attacks of opportunity.
Don't forget that while the tumble skill does offer the DC 35 stand-from-prone-without-AOO feature, it also offers the more mundane DC 15 "Tumble at one-half speed as part of normal movement, provoking no attacks of opportunity while doing so." Now, while you're prone you move slowly (5' as a move action, or 10' total if you use both your move & standard action), so using tumble will only let you get 5' away with no attacks of opportunity. Still, 5' will get you to a mostly safe position.
Also, if you follow the rule that your movement cannot be reduced below 5' then you'd technically be able to take a tumbling crawl as a 5' move, then still have a standard action left for standing. I'm not clear on the rules for that one.
You can also take a -10 to your tumble check to move at full speed. So a tumbling crawl with a DC of 25 would get you 10 feet away from the crowd trying to AOO your NPC.
One last comment. You probably already know this, having played for years & years, but feats are hard to come by and shouldn't be undermined lightly. Players don't get a lot of them. When they pick one, they are really making a declaration about what kind of character they want to play. So yes, use the many tools at your fingertips to prevent the trip feat from becoming repetitive and boring. But don't trash it all the time. That feat needs to work sometimes. If it doesn't, that player is going to feel robbed, and your game will have a downward spiral as people become too discouraged to maintain interest.
Good luck. Have fun.
And don't forget other things too, such as dwarves being more difficult to trip, four-legged creatures being impossible or super-difficult to trip, distance attacks, escape mechanisms such as the "panic button" from Complete Scoundrel, etc.
For example, anyone tripped can escape with any number of spells. In fact, this happened in a game my friend Sam ran a few weeks ago. I was playing an Abrupt Jaunt wizard (free 10' teleport as an immediate action). I also had the 1st-level spell Benign Transposition. When an ally was down and surrounded, I cast the spell to swap places, and then teleported away. If my PC can do it, the bad guys certainly ought to be able to do it.
(Technically, there are two ways to rule on how Benign Transposition works. You can say that the two characters swapping places are literally swapped right down to position of limbs -- the prone guy ends up standing where the wizard stood, and the wizard ends up lying on the ground where the prone guy fell. In that case, you need a second "thing" you can do to get the wizard away from the bad guys, such as the Abrupt Jaunt teleport feature I mentioned. However, most DMs seem to rule that Benign Transposition works like this: the spell simply swaps squares -- so the prone guy ends up where the wizard was, but still prone, and the wizard ends up where the prone guy was, but still standing. If you rule that way, then that spell alone is good enough to save a prone NPC. The downed character will disappear and reappear wherever the wizard was, still prone but not surrounded. And the wizard will appear in the surrounded position, but he will not be prone so no worries about AOO. Knight's Move is a similar spell that requires the character to teleport into a square that would flank a bad guy, but it doesn't require any characters to swap places. Also, it's a swift action spell, which means the fallen character can cast it on the ground without provoking attacks of opportunity, and then instantly transport away from the crowd. He would still be prone upon arriving at his new location, and he'd be next to a bad guy, but one bad guy is better than 5.)
Other spells like the darkness and mist spells will help. Swift Invisibility from the Spell Compendium would allow a character to turn invisible (swift spells do NOT provoke AOO, so it's safe to cast it), and once invisible the bad guy could crawl away or stand without provoking any attacks. Another swift spell, Lightfoot, blocks attacks of opportunity.
Don't forget that while the tumble skill does offer the DC 35 stand-from-prone-without-AOO feature, it also offers the more mundane DC 15 "Tumble at one-half speed as part of normal movement, provoking no attacks of opportunity while doing so." Now, while you're prone you move slowly (5' as a move action, or 10' total if you use both your move & standard action), so using tumble will only let you get 5' away with no attacks of opportunity. Still, 5' will get you to a mostly safe position.
Also, if you follow the rule that your movement cannot be reduced below 5' then you'd technically be able to take a tumbling crawl as a 5' move, then still have a standard action left for standing. I'm not clear on the rules for that one.
You can also take a -10 to your tumble check to move at full speed. So a tumbling crawl with a DC of 25 would get you 10 feet away from the crowd trying to AOO your NPC.
One last comment. You probably already know this, having played for years & years, but feats are hard to come by and shouldn't be undermined lightly. Players don't get a lot of them. When they pick one, they are really making a declaration about what kind of character they want to play. So yes, use the many tools at your fingertips to prevent the trip feat from becoming repetitive and boring. But don't trash it all the time. That feat needs to work sometimes. If it doesn't, that player is going to feel robbed, and your game will have a downward spiral as people become too discouraged to maintain interest.
Good luck. Have fun.