Buy.com offers the IOGEAR Multimedia Wireless Keyboard, model no. GKM561R, for $34.95 with free shipping. That's the lowest total price we could find by $8 and the best non-rebate price we've seen. (We saw it for $4 less after rebate two weeks ago, since expired.) This 2.4GHz keyboard features a laser trackball, scroll wheel, 19 multimedia hotkeys, on/off switch for battery conservation, and more. It requires two AA batteries (included).

Note that while this keyboard is Mac compatible, the multimedia hot keys are not supported.