I bought the 3rd gen on my last trip to Vegas for ~ £320. Was slighty gutted it was the 'latest' iPad for only a month (thanks Apple!). Although the 4th gen is not much of an upgrade. I have the 16GB wifi. I don't need the celular one, just tether it to my Galaxy S2 if I need to use it while out and about
I find I am using it all the time. Don't enjoy browsing on my phone anymore! Great for watching iplayer or movies in the lunch break
You may as well go for the latest as the older ones don't sell for much less.