Rafe and I enjoyed playing around with Muxtape yesterday (review), but were turned off by the uploader and potential limited life span of the service due to its lenient position on copyrights. If you're looking for a slightly more flashy experience, and one that works without having to upload 50MB of music from your hard drive, check out Mixwit. It lets you create gorgeous-looking Web mix tapes to share with others and pulls in media from various streaming services such as Seeqpod and SkreemR.
Maybe its greatest asset is that the players look like real compact cassette tapes, with moving spools to match how far you are through the mix and each song. You can tweak the look and feel of the tape, the font, and the playlist with a wonderfully simple Flex editor. If you feel like going back to make changes, you can also go in and add, reorder, or get rid of songs that don't make the cut.
The one bummer is that linking to playlists is not as simple as an affair as it is on Muxtape, which gives you your own personal URL. The upside is that you can create multiple mixes using a central account.
Mixwit tapes can be embedded in all the major social networks, along with any regular blog, which I've done below.
See also: Create viral mixtapes with Fuzz