I have found Kim Topley's J2ME in a Nutshell (O'Reilly) very useful.
(I haven't read Jonathan Knudsen's book yet, but I imagine it would be very good too, judging by his other writings.)
Chihuahua - Ajax-powered online word puzzle, <a href="http://chi.lexigame.com" target="_blank" rel="nofollow">http://chi.lexigame.com</a> <br />Letterbox Word Game Online, <a href="http://letterbox.lexigame.com" target="_blank" rel="nofollow">http://letterbox.lexigame.com</a> <br />Lexi Word Game for Java-enabled phones, <a href="http://www.lexigame.com" target="_blank" rel="nofollow">http://www.lexigame.com</a>
I'm using Core Javaby John Muchow to learn J2ME. As mentioned it covers MIDP 1.0, so I don't know how difficult it will be to jump to MIDP 2.0 as it becomes more popular.