(cross-post from Nifty)
Here's some ways I can think of. I will strive to list only the methods that will not rob you of your sweet, sweet levels to that demonic bandit known as ECL.
Be a frog: The Planar Handbook, and perhaps some other sources, have ECL 0 races like
these frog guys. Yep, isn't it cool that the plane of Chaos itself spawns so many frog races? That's CHAOTIC!
At any rate, Frog Guys are actually pretty good for their ECL of nothing. +2 natty armor, proficiency with the annulat (who know what it does, but you get it just for the hell of it), and the ability to rob someone of their dex bonus if you're charging them or throwing a weapon at them.
Oh yeah, and since you're an outsider, you're proficient with all martial weapons.
downside: Dying sucks bad for you. It's really hard to raise a straight-up normal Outsider.
Play Forgotten Realms: And take one of the best feats I've ever seen in a book, Otherworldly, from the Player's Guide to Faerun. You have to take it at first level, and you have to be from certain regions. The easiest is probably an elf, but the other options (Deep Imaskari and Spirit Folk) might be viable too. I don't know much about Spirit Fold, but those
Deep Imaskari guys are pretty respectable for an ECL of 0.
What's the feat give you? Well, you get a +2 Diplomacy bonus. How cool is that?
Not very? Fine, be that way. You're also a Native Outsider. That means you get all the pimpin' powers of being an outsider, and none of the grief when you kick the bucket.
downside: Richard Baker, the guy that wrote this feat, refuses to admit that it gives you the numerous perks that being an Outsider grants, such as proficiency with all martial weapons. Oddly enough, errata to the Players Guide to Faerun has come out, giving Richard the perfect chance to change this feat such that he'd be right--but he didn't. In the mean time, though, taking this feat might mean that some people that are prowling the WotC boards might give you grief about trying to use martial weapons, for example. Of course, this doesn't matter if the people in your play group either don't scan the boards, or aren't dumb.
Prestige Classes: A lot of perfectly respectable PrCs, such as the Contemplative, grant you Outsider status at some point in their progression, and it's usually Native Outsider to boot.
downside: You might have to suck up the opportunity cost of choosing one PrC instead of another. With the Contemplative, that's not all that horrible; still, though, if you have your heart set on a particular PrC, having to take up to 10 levels of another one instead can be annoying. Also note that this will only grant you Outsider status late in your career.
High-Level Magic: Polymorph Any Object and Shapechange can actually grant you Outsider status.
downside: Yeah...at like level 15 or 17. Good luck finding the hypothetical wizard out there that will Poly Any Object you at some earlier point in time.
Edit: Freakin' code not transferring perfectly from Nifty...try this, Boulie.