There are two joke websites I recommend:
http://www.inhis.com/avantgo.asp - InHis.com Joke of the Day - There's a new joke every day or so. The joke doesn't always get updated daily, but the jokes are pretty good and the price is right!
http://www.caerleon.us/hb/mobile/ - Humor Break - This web site has ten jokes. A new one is added daily every Mon-Fri and the oldest one removed.