There's great book about meaning of life, by Viktor Frankl: "Man's Search for Meaning". Really worth reading.

As for my meaning, it's something between my self development and doing my job. I'm a librarian in academic library and I always consider grades of "my" students as part of my job. I have my dark days, but most of the time I can't wait to go to work (even on mondays!). My own self-development is a big part of this, because I think that what I represent by myself is part of the library I work for.

Every "thank you", smile, everytime I hear that I helped somebody - those are my "lights" in life.