Hi Ollie
The two MIDI controllers that are generally used with LivePRO are the Novation SL Remote Zero or the Behringer BCF2000. I have used both and slightly prefer the Behringer, but that is really down to personal preference.
As Randy said, I would certainly consider the first essential accessory for LivePRO is a decent touchscreen monitor for quickly selecting and changing cues. The MIDI controller allows you to add all the bells and whistles, and whilst they're really useful I wouldn't consider them an absolutely essential bit of kit, especially if you're on a limited budget.
If you're coming to the UKLEM you'll get an opportunity to see (and have a play with) plenty of touchscreens and MIDI controllers 
Cheers
Jem
Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.”... Douglas Adams 1952 - 2001