I've created some packages for Debian on i386 and amd64. They can be found at http://mosquitto.org/files/binary/debian/. They are almost identical to the Ubuntu packages (Debian doesn't use upstart, so there is a different init script), but compiled against Debian testing (Squeeze) instead. This is because Debian 5 (Lenny) doesn't include a recent enough version of sqlite3.
Please let me know if you have any problems with the packages.