trail shoes

Another vote for the Brooks Cascadia 3.  I have them and absolutely love them.  I have done up to 33 miles at a time in them and really like them - here they are:

http://www.brooksrunning.com/prod.php?p=1100461D

Very comfy but also good stability.  Hope this helps.

Brian

What kind of trail/surface do you expect to be on the most?  If it's not too technical dirt/gravel, road shoes might work just fine for you.  If your trails are more technical, look for a trail shoe designed for your typical terrain.  If you're running on lots of rocks, you might want to look for a shoe with a protective plate to protect your foot from rocks/projections, such as in the Cascadia some others have recommended.  If you'll be on a soft surface or wet/muddy trails, look for something with a more aggressive tread.

The trails I run tend to be mostly dirt, with some miles of rocks and tree roots, and occassional mud.  Since I was using Books Adrenaline road shoes, I went with the Brooks Adrenaline ASR trail shoe, and have been pretty happy with them.  They are a support shoe, which works well for me.  On the downside, on the occasions when I find myself on mud, the not-so-aggressive tread leaves me a bit wanting.

You might consider perusing the Trail Running forum at Runner's World to search for threads on the subject.

The New Balance 900 series is a trail shoe with stability.   I had used NB 907 or 908's up til this year, but they've made them to wimpy for real trail use and it's turned into a road shoe with dark colors and offers no protection from rocks on the underside as did previous versions that I was real happy with.  Some runs that included gravel became quite painful this past summer and fall.

I used a pair of Vasque for my trail mary, great rock protection, but not enough cushioning for me.  Now I'm trying a pair of Keen Wasatch Crest which I really enjoy but they were a closeout, so I'm not sure what Keen has plans for in there line, but they seem to have good cushioning and a tough enough sole to prevent the pain caused by rocks and gravel.

There are a lot of trail shoes out there, hopefully you can find something you like and works for your needs.  The local run shops around here don't have a lot of trail shoes, and then there's REI and I don't find most of there sales staff to be a great source for trail running shoes for longer distances.  Hiking and walking yes, trail running not so much.  Maybe your local store will be better stocked for trail runners.

Are you sure you need trail runners? I ran a 100 miler and used regular shoes without too much problem...that being said I've also run many ultras where they were very necessary.

 I like, in no particular order

Brooks cascadia....not real cushioned though

Puma trail fox...light weight and cool looking

Go Lite...anything they make, very light, aggressive tread and sooper comfy, but take a little getting used to because of the aggressive tread.

Vasque are also nice but I find them to be very stiff.

 Good luck and good luck in your ultra!!

Vasque are also nice but I find them to be very stiff.

^agree and they aren't very cushioned

I just replaced my Vasque Blur with the Mizuno Wave Ascend 4.  I love running in these.  Very cushioned and great traction.