That sounds awesome. I'm getting a full suspension trail bike and I'm excited about turning my xc hardtail into a commuter/urban bike.Funny you should ask. About 20 years ago, I already had 3 bikes but they were all lousy for commuting. 2 road bikes and a mountain bike. I decided to build myself a custom commuter.
I bought a mountain bike frame from a shop that someone stripped for parts - $150. Then I coated the inside with linseed oil and left it hanging in the garage for 2 months over the summer until the oil dried - rust proofing - you never know. Then I built up the bike up with older mtn bike components off the Cannondale I ride. I put on drop handlebars from a road bike and bar-end shifters ($80). I wanted to put on road STI brake shifters, but they were too expensive at that time ($500+). For tires, I highly recommend Specialized Fat Boys - the only tires that I know that contain a belt and are rated for 100 psi.
I actually have 2 sets of rims - one with slicks and one with mtn bike tires. I take it off road as well. Lot easier to swap rims rather than tires for bad weather or change of riding venue..
Been riding that bike for over 20 years and it rides fast and precise. I can hop curbs like a mtn bike, yet fly down the road like a road bike. The nice thing is that it looks like some kind of a weird road bike, so the bike thieves haven't bothered me much. Looks even weirder with mtn bike tires.
Can't post a picture though - I have it out for servicing. After 20 years of riding and doing my own maintenance, I figured that I better have a pro go over it and strip it down for an overhaul.
The best commuter is one that you create yourself by adding the features you'd think it should have.