I have a problem with the length issue too - I'm 5'9". I can get by with most if I'm only going to wear flats with them, which is primarily what I do. Gap, Eddie Bauer and J. Crew all offer inseams up to something like 37". I prefer Gap and theirs tend to run around $50, less when you catch a sale. Even Gap's regular length is around 32" on the inseam, I think.

An even bigger problem for me is finding yoga pants that are long enough. I finally found a place online that offers longer lengths, but they're really expensive.