Im assuming the A2 has a single DIN slot - if so - get the Pioneer P77MP - absolutely class headunit. Looks classy - not tacky, a subtle screen and packed with features. Excellent sound quality and a good in-built MP3/CD player. I've connected an iPod cable to the rear via the Aux in and that sounds awesome.
I got two of these off ebay (got a bit overzealous with my bid sniper!) for £94 and £112 respectively - mint/good condition, in the space of a week.
Sold the £94 one (Slightly marked round the edge of the facial vs the £112 one) for £145 on an audio forum a week later.
They should be even cheaper now the new range of Pioneer HUs are out now.
