I spent the first two years of living in Tokyo somewhat isolated from other people working in the tech creative space, and I remember how happy I was when I finally stumbled across the now retired "Tokyo Two Point Zero" event. Back then there was no meet up.com or twitter etc. so meeting new like minded people was somewhat harder than it is now.
Nevertheless I still get asked this question a lot, so if you're in the tech/creative space and new(isn) to Tokyo here's some ideas:
@CheapoGreg wrote a great article on Start up events for English Speakers in Tokyo
And my personal picks from this list would be:
UX Talk Tokyo - very popular now!
Ride The Lightening
Pechakucha Tokyo - monthly event with creative peeps presenting their projects (also the venue SuperDeluxe is a pretty good spot for meeting creative types)
There's a facebook group for Tokyo Start Up events (which are mostly in Japanese)
And there's our own Tokyo Cheapo monthly meet up Downtown drinks, though not specifically tech/creative tends to have a quite a few turn up every time.
Also there's meetup.com too.
On the internets
You can search for people on twitter obviously, some people have saved you the trouble and created lists like this
Canvas is a new community for Tokyo Creatives, it is invite only but you can request an invite.
Anyone else have any suggestions?