If your budget is £100 and you want something decent that's easy to use I would go for the JVC KDG311. £99.99 from Halfords. Or the KDG111 if you dont want/need mp3 playback - £69.99.
get a sony cdx f7700 cd/mp3 player, it is the nuts, they would be just over your budget at 100 quid for a new one but you could get the f7500 cd/mp3 for 100 quid
Head unit came today, fitted easily (except for the bastard Autoleads facsia adapter :bang: ) and works awesomely (is that even a word? ) . Loads of features, and sound quality is great (partly thanks to my sexy new Infinty speakers . And for £99 with the remote I doubt you could get much better value!
From me this HU gets a Kanye West "2 Thumbs Up"
P.S. I saw this same HU in Halfords on Saturday at "Half Price". It was £150 without the remote