This has been done here quite a few times.
I think that if you want a GPS moving map on a PDA (which means a Palm or Pocket/PC device) and you want something approaching usable European coverage (rather than US-only) then you are limited to
1. Memory Map (aviation charts for UK only; they have the CAA charts)
2. Oziexplorer (you have to scan in your own charts from e.g. the printed ones)
3. PocketFMS (an "open source"-type project)
If however you mean "PDA" loosely then there are also tablet PCs. The smallest current one is perhaps the Motion LS800 (do a google). These will run all of the above, plus Navbox, Jeppview (Flitedeck), Flitemap (no longer sold), and probably other stuff I don't know about.
My personal view, having played with PDAs, is that they are of very limited use when flying. The screens are small, not sunlight readable, the touch screens are prone to accidental touching, and the buttons are too fiddly.
If I was buying a VFR GPS today I would get the Avmap EKP IV, without a doubt.