The best way to earn miles (w/o flying) is to sign up for the Dining Program that is affiliated with your favorite airline (almost all major airlines have that option for earning miles). It is run through the Rewards Network, and after you've dined at their participating restaurants (nationwide and Canada!) a certain amount of times, you earn an elite status (similar to airline programs) and begin to rack up more miles (starting at 1-3 miles per dollar (incl. tax and tip!) and going up to 10 miles per dollar) ^ . If you have an airline affiliated card (CO, AA, UA, etc...), then you get that extra mile for charging on that card ^ ^ . What's nice is that you can add as many cards as you want to the program. I've been taking friends out for years and paying for the bill (while getting the cash from their portion of the check and going to the bank) and racking up serious miles....

The best card I've found so far is the Citi PremierPass Elite card - points, not miles and discounts for gas, Rx, grocery, etc....and the initial bonus of 15K points doesn't hurt either.