WiFiTunes (http://www.aspecto-software.com/rw/applications/wifitunes/) is a DAAP client in the sense that it connects to a DAAP server and streams music off it.
…Actually, only mp3 files.
…And, now that I think about it, it’s closed-source, slow, crashes a lot, and severely limited.
But, on the bright side, it’s the only option I know of for Windows Mobile-powered smartphones and PDAs. And if all you want to do is listen to mp3s in your library, it works. Usually.
My favorite feature is when you try to play a song larger than about 10 MB, the program skips to the next song, as it’s written to store the entire file in program memory (which is severely limited in Windows Mobile).