We have similar politics and views on the world.
We both love making music and we met through a shared love of singing <geek alert>
We have a very similar sense of humour.
I guess we're both 'above average' IQ although he's much cleverer than me.
We both love to be outdoors: hiking, camping etc.
We're both Londoners through and through and love our city.
I like to plan and be organised, he's so laid back he's horizontal.
I enjoy much more 'light' entertainment e.g. musicals. He's keen on avant garde stuff.
He likes things like Lost, 24, the Wire. I live Everwood, Location Location and Supernanny. We used to both watch ER but that's finished now so the only TV show left we both like & watch together is The Daily Show!
He is a big sports fan, I am not interested in any of it.
He runs, I swim.
I think we complement each other pretty well though. He's put up with me for 8 1/2 years so far anyway 
ETA We both had similar upbringings (lower middle class, 'hippy' liberal parents) literally down the road from each other, which means we have lots of shared/common childhood memories and seem (so far) to have similar 'long term views' on life.