One that I always thought would sound great on ukulele because it's a strummy, acoustic number (played on guitar of course) is #9 Dream from 1974's Walls & Bridges. There are tabs in the usual places -- like here -- and the chords are pretty easy (well, plus an E lol) but this is a song that feels like a long way between the tabs and reality. Maybe there are some inversions I'm missing or something? Anyone taken a stab at this?
The UkuleleUnderground.com website has a lot of tutorials and play-along videos. Here are a couple of John Lennon songs (I'm sure there are more). The first one is rated beginner and the second one is harder.