Chores & Allowance

In the early days, there were no chores for the kiddos. No expectations of the children regarding contributions to the family. Since then, I've bought into the theory that everyone needs to do their share. Children are capable of doing chores. That said, I have a question about allowance. Should allowance be tied to chores? What is effective motivation?

We give our son lunch money every week - more than enough to cover daily meals at the school. He usually has money left over, or can manage his spending during the week to pay for the occasional extra activity. Tonight, he paid his way to see a school play. We expect him to get his chores done every week, but the weekly lunch money is not considered an allowance. If he doesn't get his chores done, he still gets lunch money. It's been hard to keep him motivated to do his chores, much less anything above & beyond to cover extra expenses.

Chores have been a long standing battle and too much nagging seems required to make sure they're done every week. I've tried a variety of approaches for motivation, including making lunch money (allowance) conditional pending chore completion (that didn't last). I'm interested in your thoughts.