Roger Przytulski wrote a pretty cool duet for alto and flute. It's pretty accessible. It's called chamber dances. 4 movements. you can check out a full recording of it here...
http://www.rogerprzytulski.com/works.html I'm working on it right now with a friend here to play this summer at wildacres.
Gregory Wanamaker wrote a GREAT duet for alto and clarinet. By great, I really mean amazing. It was written for Dr. Timothy McAllister (sax) and Dr. Alan Woy (clarinet) who were both teaching at Potsdam at the time. You can hear the first mvt here by those two...
http://gregorywanamaker.com/mp3/index.html I'm also working on this one for a performance at the end of the month. Just be warned, the first 3 movements are pretty accessible. The first mvt has some really tricky stuff, and you need to be able to use non-conventional fingerings (i.e: flipping F to F#; sliding bis Bb to B, etc...) or it'll be a lot more trouble than it's worth. The 2nd mvt is BEAUTIFUL!! The third mvt, I'm not a fan of. We read half of it once and decided not to worry about it. Haha... the 4th mvt, though.. is very hard. You have to be able to play VERY independently. The sax part also has slaptongue, multiphonics, and some altissimo. Just some key things to be aware of. So far, this is my favorite duet, period.