Scout (CAdv) could be really good for this--you get speed bonuses, combat benefits from moving, and a pile of skill points. All the movement optimizing tricks for scouts apply (Swift Hunter potentially, Travel Devotion definitely, etc). It also means you could make your combat gimmick "runs around in all kinds of bizarre places, and gets some bonus damage out of it".

Otherwise monk's speed bonuses could be really valuable, though the class is pretty weak. Swordmage is a good replacement, though I don't think gets the same kind of free movement. A level of Barbarian for the +10' boost (and some extra BAB/hp) could be welcome as well.

Lots of options, depends on what exactly you want to do.

edit: swordsage. I always replace one with the other :p

Unfortunately, that book isn't available to me and I don't know much about the Scout class, but it sounds perfect.

Books available. PH, DMG, MM (3.0 and 3.5). The 3.0 softcover splat books and Complete Warrior. Also, Forgotten Realms, Eberron, Wheel of Time (don't know why, but it is available.

I know monk would work well for the free-running, but their other abilities aren't what I'm picturing. I just can't see the free-runner as a really strong martial artist, but that's just my conception.

Well that's going to make things more difficult :p

IMO, when making a D&D character, you generally have to have some kind of gimmick/method for doing "combat", since so much of the game is based around that. Scout would give you a strategy for that.

Otherwise, I'd say go with Rogue dipping Barbarian for the speed boost. Monks suck a lot in 3.5--their "attack" mechanic is based on full attacks, requiring them to stand still. They really aren't great skirmishers. At least with a rogue you could do a hit-and-run tactic and get some sneak attack damage from a flank. The monk isn't going to help much, other than with the speed boost (which doesn't help much by itself).

Also note that you can play a monk and not make him a "martial artist". Maybe he runs around and smacks people with a staff, or causes them to be damaged from falling beams or whatnot (just reflavor his unarmed attacks as coming from something else). If you want to play this kind of concept without the mechanical basis to support it (ie, without a good spread of splats and character options), you're likely going to need to do some reflavoring.

I really like the flavour of the martial artist whose attacks come from elsewhere. That's a great way to flavour it out.

As far as combat goes, I'm always confident that I can do something in combat; I'm pretty creative in what I do usually and I wouldn't try to stand up and fight full attacks generally with either a monk or a rogue. There's always a way to use a rogue creatively in combat and I know from past play that I can do that. Dodge/mobility/spring attack with tumble is always an option and even fits the concept pretty well.

Thanks a lot, you've given me a lot to think about. I like the dip of barbarian for the speed, and I'll think about that.

The Thief-Acrobat from Complete Adventurer sounds like it would be perfect. I'm not sure how it compares to the 3.0 version from Song and Silence. Five levels of Scout from the same book should get you all the prereqs, as well as a speed boost and bonuses to AC and damage when moving.

You might also want to check out some of the movement skill tricks from Complete Scoundrel. There's even a feat in that book called "Freerunner", although all it does is increase the number of movement skill tricks you can learn.

I played a monk (+lvl 1 barb) with this in mind for a bit. Boots of Springing and Striding are a must-have. I had a lot of trouble dealing real damage, but I did find that I was quite helpful in stopping enemy spellcasters, as I could get to them super fast and tackle them (Improved Grapple) -- keeping them busy while the party dealt damage.

At one point, my character was blinded by a trap right before a boss fight... that sucked. Since I couldn't tell where anything was, I asked one of our other characters (a psion) to "throw" me at the boss -- I was intending to grapple blind, assuming my thrower 'hit'. Unfortunately, my thrower rolled a 1 and I smacked the back wall of the cavern and was out for the fight.

Hahaha, your DM allowed you to multiclass monk/barbarian? Broken.

1st level Barbarian, 5th level Monk. Trust me, it was NOT broken. In fact, that character sucked... in combat at least. She was able to move around the battlefield and over/past obstacles with little problem.

In one case we were tracking a lich in some underground caves. The lich retreated at one point, knocking down a bridge (wooden plank) over a 30 ft gap. We were in hot pursuit and I was in the lead (since I was the fastest in the group by far). I jumped the gap with little problem.

Of course, this meant I was one-on-one with the vampire while the rest of the party watched me get destroyed from the other side of the gap. Grappling with an undead with a negative-level touch attack is a bad move.

Great for mobility. Terrible for combat.

Yeah, if you want good mobility and fighting in combat, you can play a longstride shifter barbarian and move 50' when shifting and take the longstride feat that gives +10' when shifting for 60' when shifting. Works even better splashed with were-touched master and fighter splashed for the feats (or ranger for concept).

I have a character like that and his jump is ridiculous, but he's also a terror in combat.

I think a monk would be very good for this type of character because when I think of a Free Runner I think of someone who wants to be as light, fast and unencumbered as possible. Monks don't need to carry heavy armor or weapons that could slow them down because they get AC bonuses and have Unarmed Strike. They also get speed bonuses for running, and their Slow Fall & Evasion feats can be very helpful if you miss your jumps.

If you want to create a thief-type character, then Rogue would be the way to go because of their lock picking and trap disarming type skills. But if you want to create a Parkour character like the one from the Mirror's Edge video game, then I think Monk would be better.

Definitely going to go lightly armoured if at all armoured, nothing more than a chain shirt for sure (maybe a mithril breastplate at higher levels, but even then probably just a mithril chain shirt).

I'm not familiar with the video game, sorry.

Thank you for your feedback, everyone, I appreciate the ideas and I'll let them percolate a bit before deciding what I'm doing.

I just a couple of days ago made a parkour based character. I used the scout model and plan to prestige into the thief acrobat. He's 5th level with the acrobatic feat and boots of acrobatics. HE doesn't wear armor and has an AC Of 15 due to +4 dex and +1 shirt. He only carries a little money, a shape-shifting longsword (into a braceltet) and some daggars on his person. With all of these he has +18 tumble, +14 climb and balance and many +12's in acrobatic scores.