I’ve known about Konfabulator, which is now the Yahoo Widget Engine, for quite some time, but I never installed it. I just figured I already had enough stuff on my desktop. But I took it for a spin yesterday, and I”m liking it. Picture Frame is probably my favorite widget right now. It supplies a rotating image feed from your flickr account or from a folder on the desktop. If you use flickr as a source, you can choose your photos, everyone’s photos, or just your favorited pix (I wish it would let me do mine + my favorites, but no dice). I run this one at work and it produces the same affect that having a bunch of pictures of your family and friends would. The “head’s up” display option is especially nice, in that you can set certain widgets to only display in this mode. I have several that I only want to look at when I first log on. This way you get the advantage of them w/o eating up so much screen space. It’s for Mac and Windows. If you run Linux + KDE, you might try SuperKaramba.
If you run Windows and you’re not into endless system tweaking but you’d still like to modify the look of your folders and color code them (a feature that was standard on Mac OS 7.0, if I remember correctly, but still isn’t an option under XP), iColorFolder is an elegant solution. It gives you a nice context menu for switching folder icons and setting colors. It comes with some very nice icons (organized into sets or “skins”), though you can use any you like. The current version uses .NET (Mono or the official version), but the author is going to recode it in C++, which will make it native Windows app.