For those who don't know (where have you been?). He played the engineer for the starship Enterprise in the original Star Trek TV series as well as the first 6 Star Trek feature films.
There's a tribute to him on StarTrek.com.
I can happily say that Star Trek is what got my geekdom started and a Star Trek convention was the first convention I've ever attended. I really wish I was able to see him in person at one of those conventions.
I think it's time for a Star Trek movie marathon tonight.
You will be missed. :(