Get out early!
The usual advice is to go after Labour day - schools return, so wildlife comes out to play!
The alternative is to be out at dawn - thats the best viewing time - get breakfast later.
Try the trails - even a few hundred yards away from the road, its a different world.
There are some smaller roads - well worth visiting if they are open.
Check out the Yellowstone Association courses - they often cost little more than the hotels and give expert guides and transport.
http://yellowstoneassociation.org/insti ... dging.aspxOld Faithful Snow Lodge is the best hotel. Roosevelt & Mammoth are in the best area near Lamar for wildlife viewing.
When you go back to Yellowstone (and you will!) try Winter! - its spectacular!
What are your main interests? Wildlife? Geology? Geysers? Scenery? Yellowstone has it all - different places are best for different things.
Finally - chat to the Rangers - they know what is where when! They will be slow to tell you where to find bear but most other things they can be very helpful.