Pompetamine/Croix de Fer (are there more like these? Cheaper ones?) are probably what you're looking for. They're more expensive than a cheap low end mtb but will last longer due to better quality parts. Hub gears are also nice on a commuter. You can choose from either cross tyres, touring tyres or skinny road tyres, whichever you choose will greatly impact the ride quality and speed. Riding position will be much better suited to your needs. Don't get one of the bikes scoble suggested, they are basically mtb's bodged into something they're not and will never be as good, but do cost as much or more than a pompetamine. Whatever you do, don't get a 29er, that doesn't even make friggin sense.
Pompetamine/Croix de Fer (are there more like these? Cheaper ones?) are probably what you're looking for. They're more expensive than a cheap low end mtb but will last longer due to better quality parts. Hub gears are also nice on a commuter. You can choose from either cross tyres, touring tyres or skinny road tyres, whichever you choose will greatly impact the ride quality and speed. Riding position will be much better suited to your needs. Don't get one of the bikes scoble suggested, they are basically mtb's bodged into something they're not and will never be as good, but do cost as much or more than a pompetamine. Whatever you do, don't get a 29er, that doesn't even make friggin sense.