[Dr_Fashizzle]

For old monitors, I use 1600x1200 and for widescreen I use 1920x1200. Any modern OS will scale it down smoothly to fit someone else's monitor.  Scaling up will usually get blurrry, so i try to keep it at teh largest "normal" sizes for each type of monitor.

There's a chance of either black bars or cropping on some screens, but I don't think it would be too bad. Whatever the person uses to display the wallpaper should have a zoom mode that works for them.

But, have you seen this?

gizmodo.com/5132065/philips-ultra+widescreen-219-cinema-lcd-moves-the-letterbox-bars-to-the-side

(Drool...)

[TheHerald]

Since the original link to the screen size guide was lost, I thought a new upload was in order.  

[prinz]

new computer has a 24 in wide screen moniter at 1920x1200 using a Nvida Geforce 9800 GI  card...8 gig of ram and one terabit of hard drives..quad core cpu....this should last me a few years    photoshop works really really well on this beast!