Tom Jones - met him a few years in Dublin after my mate chased him down the street singing 'Sex Bomb'. He stopped and joined in and had a chat. Very surprised with how nice he was.
Mikey Graham from Boyzone - Absolutely lovely and does not get enough credit. Shane and Ronan are also lovely.
Dermot O'Leary - Chatted for ages and was asking everyone to do Crazy Frog impressions.
I've also found Myleene Klass to be absolutely lovely and very funny.
Not so nice:
Only one encounter but Mick Hucknall has a serious attitude problem and needs to get over himself. Pushed through a crowd of us (girls) and then told us to move. Then when someone recognised him and asked for a photograph he looked them up and down before walking on.