At the moment, I have Barsoom on my PC.
http://www.themeoftheday.com/td051100.htm
I change it every couple of weeks because Tucows has so many very cool ones. Also, any of the themes by CyberGypsy, especially his Egyptian motifs. Unfortunatly, I no longer have the URL for his stuff. 
crap
lemme try that again
Mind is of the characters Willow and Tara from Buffy the Vampire Slayer.
It inspires me.
Here’s a picture of my old 6100 PowerMac, complete with Yosemite wallpaper. (What else?) My iMac also has Yosemite wallpaper, and my laptop (which I am using now) has this nice picture I took of Yosemite’s Merced River. My PC has a picture from the film “What Dreams May Come”. A friend put it on, I like it. When I do change the wallpaper, it’ll be…Yosemite wallpaper. (Like you had to ask!)
I have a marvelous high resoulution artwork image from this site, a museum’s collection of it’s paintings.
** http://www.thinker.org/fam/thinker.html **
Both at home and at work, mine are changed quite frequently. Right now, here at home, my wallpaper is Renoir’s Moulin Galette:
http://hometown.aol.com/frannle/myhomepage/photo.html
(I hope I didn’t misspell that). Oh, and look at my taskbar – I just love it! Cute, huh! Oh, it’s the li’l things that make one happy. 
Mine is of the “Too Hot” chick from the Altoids commercials and print on my 21 inch monitor. Something about a totally fantastic babes looking like pinup queen works for my desktop…and my room in general.
http://www.toohot.com/Stolen/Screen3-1024.htm
http://www.toohot.com/Stolen/Screen2-1024.htm
http://www.toohot.com/Stolen/Screen1-1024.htm
All of these work groovy on a desktop
Currently a picture of Bahamut and Alexander from Final Fantasy IX.
BEAUTIFUL…
A beautiful sunrise by the sea… Who would have figured?..
I don’t change mine very often, for the past month or so I’ve had a photo of my baby niece, Amaya.
Currently, it’s from a Desktop Theme called Jeweled Night…it’s really cool, but I’ve had it so long I don’t remember where I got it.
I keep thinking I’m going to put together a theme of my own, and then I’ll change the background to the cover of Pink Floyd’s Pulse album.
As with TheNerd, I have used a solid black desktop background for years (since the days when wallpaper on a Win3X 386 would slow you down) and I’ve come to like it. At my company, we had all the machines setup that way.
Recently, though, at work, where I use a machine with 3 monitors, I’ve taken to having the daily update of the price of a barrel of NYMEX light sweet crude as a ~3" x ~4" graph on my middle monitor; the lateral monitors are still all black desktop. It’s kind of silly, really, because I almost never see it with the apps I’ve always got open.
I used to have an image of Jeff Buckley (RIP) or Tom Waits on my desktop. Recently, I changed it to a gorgeous picture that a friend of mine took from the summit of Mt. Collins, in Colorado. There’s a marvelous view, and a mountain goat in the foreground.
Oh Ogre, you’ve always been a sucker for a mountain goat.
As for me, I’ve recently been partial to any shots of the alluring Laetitia Casta in as little as possible, without crossing a line that might offend the more sensitive people in the office, resulting in my being sent home, terminated, and living in shame.
And cuddly teddy bears. Always got have the cuddly bears on the desktop. Or not.
This is my favorite wallpaper ever… I felt so lucky to find it… Meg… ahhhh… 
http://www.ggj.abelgratis.co.uk/meg/26-50/meg46.jpg
My wallpaper is our running club mascot/logo–a running turkey. http://www.turlockrunningclub.org and my screensaver I got from Runner’s World.(What did you expect?,Im a runner)
Terragen is a Terrain Generator. You can specify any number of variables (random or fixed) like clouds, light direction and intensity, colours, depth, surfaces, etc, and it will generate a 3D image for you. It’s frighteningly realistic.
My desktop is currently Angelina Jolie, as Lara Croft in the Tomb Raider movie. I’d say half the time I change my wallpaper, it’s to a Lara Croft one.
At work, I have mostly been using images from the new upcoming Star Wars movie, but in fact currently it’s a CGI image of the USS Enterprise as seen in the updated version of Star Trek: The Motion Picture which will be released later this year.
At home I have an HST shot of the Ring Nebula in Lyra, and here at work an HST shot of the Crab Nebula in Taurus… both are gorgeous images!
At home, it’s currently the poster from the upcoming film A.I. (please don’t tell Mr. Spielberg). It’s usually a movie poster of some kind–recent ones have included the teaser poster for “The Gift” and both of the posters for “The Grinch”.
At work, it was a tiled group of bumper stickers reading things like “Don’t blame me, I voted with the majority”, and “Impeach Bush (and we’ll call it even)”. Preceding that was a tiled picture of Saddam Hussein taken from thedictatorship.com for no good reason.
On an off note, bump and Astroboy14 both mentioned “HST” photos and my first thought was wondering when Hunter S Thompson started doing photography. 
