We're looking for a very nice hotel near Yellowstone to celebrate a special occasion. Any suggestions?

We stayed in West Yellowstone a couple of years ago & stayed at Hibernation Station. We really enjoyed the privacy of the individual cabins (we stayed in the Wolf Cabin, #24?), while being walking distance from downtown and very close to the west entrance to the park. It wasn't an inexpensive place, but we felt it was worth the price. Nice towels, gas fireplace in the "cabin", big bathroom, fluffy towels, large jetted tub, refrigerator, housekeeping every day, comfortable bed... It was great!

http://www.gtlc.com/lodgeJen.aspx

I think Old Faithful Inn has an absolutely charming and authentic lodge feel from the 1900s. It has many places to sit and relax in the lobby on several levels, a bar close by and a decent dining room. The standard rooms are nothing special, but they may have suites.

I did see the lobby of Jenny Lake Lodge and immediately loved the intimacy. And the Tetons provide stunning alpine scenery. Jenny Lake Lodge offers cabins around the main lodge, but I have not seen them inside. The small warm, cozy lobby and location close to the Tetons made me want to book something soon! It feels more like a B&B.

The Jackson Lake Lodge is very large and has more of a corporate feel. It has a huge sitting room on the back of the hotel with stunning (and blinding since they are direct) sunset views of the Tetons as well.

It depends on what you are looking for.
Annealex

Of course, those are not Yellowstone, but more than an hour away--I think your best bet is to look at upscale condos in the Yellowstone area. But there is nothing in the park that can be called "very nice".