Since we're resurrecting this post.

For daily user kitchen knifes: Warthog curve. A couple of quick strokes will get your knife to cut again.

For nicer knives on a budget: A Lansky. If you have exotic steels, make sure to get diamond stones. You'll spend hours trying to sharpen CPM or M390 steel with normal stones.

For nicer knives on a bigger budget: Wicked Edge pro.

For all knives when money is no object: A Tormek.