I've often thought a warming filter would be a damn cool thing to use if one came across something like a leopard in the golden glow of early morning sun- just to enhance the effect. However, I've only ever used them for portraits myself.
In the bush I usually only use 2 filters - a polariser (especially on wide angle shots including sky/water reflections) and a UV filter, simply to protect my lenses as filters are far cheaper to replace. I once saw an awesome shot of a deer in the UK, where the photographer used a "warming polariser". If you ever find such a thing on sale, please let me know!
A lot of people warn against filters for a couple of reasons. Firstly, sometimes when it's early/late, you just can't afford the light they steal (UV's aren't nearly as bad as PL's). Also, especially if you don't buy good ones, they can degrade the image. Not being a millionaire I can't afford to smash a lens though, so I usually have at least the UV protecting
There are a few decent makes out there, and multicoated is always a good idea. Hoya is about as cheap as you can go and still get a nice filter. Maybe I'm just lucky, but my Hoya circular polarisers have always given me stunning results.
Oh yes - neutral density filters. These are very cool, as they slow down the light coming in without affecting the colour. Here's an example:
(before you ask, yes, eventually that piece of grass annoyed me enough that I cloned it out for sale. We could argue ethics all day, but I'd rather clone it out than break and kill the piece of grass... probably a silly female thing
Anyway, that shot was taken in bright summer sunlight near Sabie in the Lowveld. I wanted the silky effect with the water, but was using my first digital, the Sony F707. It's lowest ISO is 100 and it's smallest aperture a mere f8, so I needed to slow things down further in order to get a longer shutter speed. I achieved this by placing a Hoya circ polariser (note, linear polarisers are not recommended for digital) on the lens, and stacking an 8x (adds 3 stops) Hoya neutral density(ND) filter on top of that. It's unfortunate I can't show you an 8x10 print - they are stunning! And that with a really tiny sensor (5MP, but the physical sensor size is very small) and two filters in front of the lens. So much for image degradation...
You also get split ND filters. These are very cool for those times when the sky is bright and the foreground dark. They are usually either 1/3 or 1/2 ND and the rest of the filter is clear. You also get them in varying density's for varying light conditions. The clear bit fades gradually into the ND bit, and you place this fading around the area of the horizon.
I've often thought it would be damn cool to get a solar eclipse filter (maybe stack two?) and take a shot during the day with the clouds moving across the sky - maybe for a couple of hours. So far all my experiments like this have been at night, but I'm thinking such filters will probably be on my birthday wishlist this year so I can give it a bash!
I hope that helps