VLC itself has a “capture desktop” mode though apparently it doesn’t work with sound. It feels a tidge slower than (if you’re on Windows) using a directshow input source that also captures the desktop.
Here’s a list of the ones I’ve found that are free to download.
https://github.com/rdp/on-screen-capture-recorder-to-video-windows-free (my own, a shameless plug–it’s free and open source!)
download it from here: https://sourceforge.net/projects/screencapturer/files/
http://www.umediaserver.net/umediaserver/download.html uscreencapture, works ok.
http://wiki.medialooks.com/Screen_Capture_DirectShow_Filter seems quick, though I haven’t looked at them too closely (note: it expires after a time trial, so after that point you can no longer use it after that time without purchasing it).
http://www.splitmedialabs.com/download pretty fast, adds a water mark to your output though unless you pay.
http://koitsu.wordpress.com/2009/09/12/how-to-install-and-use-scfh-dsf/ is said to be pretty nice. Haven’t tried it but looks good. Looks like it’s open source and LGPL licensed: https://github.com/mosamosa/SCFH-DSF (though possibly unmaintained?) and also http://mosax.sakura.ne.jp/yp4g/fswiki.cgi?page=SCFH+DSF+Dev
VidBlaster video switcher software is rumored to have a capture device.
http://www.ffsplit.com also has one (or used to, at least). It might even capture direct3d windows, it’s unclear.
http://obsproject.com/ can accept screen capture and “stream” it (doesn’t have a directshow virtual capture device, itself, AFAIK).
So far I prefer my own, the topmost one. I even take feature requests!