http://www.odyclub.com

In a nutshell:

95-98 was first gen--pretty much a tall Accord wagon with a magic seat
third row and swing-out doors.  If this is what you want, find a 98.

99-01 was the first of the large Odyssey that competes in the
Chrysler-sized market.  Stay away.  Stay far, far away.  Horrible 4
speed transmission problems, rear drums, 205hp, lesser content levels,
etc.

02-04 was the same body as the 99-01, but many items were ironed out.  
It got a 240hp engine (on regular gas, no premium required), all-new 5
speed auto transmission, rear disc brakes, improvements in the electric
sliding doors, factory optional leather and DVD/rear entertainment, etc.

That being said, this transmission was subject to a recall of its own.  
It wasn't until the middle of the 04 model year that all the
transmission bugs were hammered out.

05 saw a model change, refining the feature set even more and bumping up
horsepower and giving cylinder deactivation in the higher models.

02 is the first year I'd consider.