Just checking my email now, I see that I told Ben Smith a year ago that I had a 31" waist, when sizing my down pants. Funny, all my jeans and pants which are sized 30" require a belt. That's some hefty inflation for ya ;)
Anyhow, Chris, what kind of pants are you looking for? Outdoor pants? zip off pants? dress/work pants?
Most of my outdoor stuff has some elasticity to the waist, so I usually just opt for a size small, or 30, and they fit is great. This is especially true with my running shorts.
I'm a string bean like you, at only 5'9" 132-138lbs,
I've tried the following pants, with great results:
Wind pants: Montbell Dyanamo
Running shorts: Just about any brand in small
Durable traditional shorts: Prana
Zip off pants: MHW Mesa (Surprisingly, seeing as Columbia is their parent company, and their stuff is ridiculously baggy)
Soft shells: Marmot Scree (very athletically cut, to my surprise)
Work pants: J. Crew urban slim fit :)
In general, I can also fit into a Youth Large for pants
And as others have mentioned, British/Euro Brands like Montane, Rab, CampUSA are great bets.