Most Profitable Herb

What is the most profitable (legal) herb that I can grow indoors with a small system. One that you could dry or sell fresh to gourmet restaurants?

Probably fresh basil. Don't bother trying dried herbs – you will never be able to compete with large scale field producers. But, good quality fresh basil is a problem in many areas, and if you can provide a consistent, year-round supply, you are likely to find customers.
Some additional reference material you should consult:
1) Lee Sturdivant's book "Profits from Your Backyard Herb Garden" covers small-scale commercial fresh-cut herb production and marketing; and 2) Richters 1996 Commercial Herb Growing Conference Transcripts. Both Ian Adamson, speaking about basil production, and David Cohlmeyer, speaking about fresh-cut herbs and salad greens, have valuable tips you can apply to your nascent herb business.