I love my Surly Cross Check, and my friends with Surlys (e.g., Trucker) love them. They're tough and versatile, and relatively inexpensive for the value. I've had mine for 15 years and use it both for kicking around town and for all sorts of road and gravel-road riding. For years I commuted to work on it, I've shipped it across the country to ride while traveling, and I've even done a few mountainous century rides on it (Tahoe and Sierra Nevadas). It's also great in the winter because the wider tires and steel frame stand up to ice and road grime. You won't be able to ride their cyclocross or touring bikes on technical mountain bike trails, but I've occasionally taken mine off-road on some bumpy, rutted old logging roads and it's been fine.
I don't recommend a mountain bike for a 10-mile commute... mountain bikes are heavy, and even skinnier mountain bike tires don't roll efficiently on roads.
If you want to buy used, you can probably find some Surly bikes on Craigslist, eBay, or Pinkbike -- e.g., I just saw a nice Long-haul Trucker for sale on my local Craigslist site. Tempting, because it was a good-looking bike! But then I remembered how much I love my trusty old Surly.