Hi Paulos66. It sounds like your son has got off to a good start music-wise. He's in safe hands! The problem I have found as my 2 girls (9 and 6) get older is that they start to develop their own taste. Whereas once it was all Zep ac/dc and the Beatles, it is now Hannah Montana and High School Musical. Having said that, co-incidently, my youngest was enjoying Dazed and Confused on my ipod the other day (well, the beginning of it any way). There are only 2 types of music, good and bad and this covers all genres (with the exception of modern R&B obviously). There's some great pop out there old and new and there's some godawful rock. Try and keep as broad a selection as possible, classical, disco, jazz, house, funk, blues etc.etc. and try and show him the difference between 'good' music and 'bad'.
As for a suggestion as to what to play tonight, how about some classic (60's-70's) Stevie Wonder, that always goes down well. Or The Who, Quadrophenia has some great 'marching' music on it. Or the aforementioned AC/DC's Back in Black. Or any Beatles. Or Zep. Or Talking Heads. Or...