I own an Archos 605, which in my eyes is a great PMP.
It can play DivX (with mp3 audio, for aac you will need a plug-in for about 20€) without conversion, but only at DVD quality max (given it has the same screen as the Pandora playing back a 720p movie would not make much sense anyway) - it can also play most other formats right out of the box (but none at 720p).
Since then it has been surpassed by the Archos 5 and probably an even more recent model which might be able to play 720p movies.
It also can play Flash contents has built-in WiFi and the mobile Opera browser with widget support.
You can also get several peripherals for it.
It is a Linux based OS with a some propreitary front-end, but you can get a "community patch" which gives you root access to install any OS you want - but for general PMP use the default OS is already pretty good.
Anyway, the device is great, but comes at a cost - at least 300€ (back then for my 605, recent models are probably at the same price).
You might be able to snatch an used Archos5 for under 200€.
http://www.archos.com/
Btw, I highly doubt the Dingoo can play 720p movies given it has little CPU power - you will need a pretty good CPU to play 720p flawlessly.
The Archos website states the Archos5 can at least play some video formats up to 720p (you can find it under Android Tablet - apparently they only sell them with Android now).
foxblock out
EDIT: I dunno if that was just a different example, but are you aware that 720p is 1280×720 and not 720x480 (which is 480p)? - 480p seems much more likely to be played by devices mentioned here.