For me the biggest mileage earner other than flying is the use of credit cards that give miles. If you are committed to CO, you probably already have a CO Chase Mastercard. But if you don't, check around and see what the best options are for sign-up bonus miles. There are several different cards that Chase offers and you can often get more than one. Your wife can probably also get one and get the sign-up bonus miles as well. I find it is worth it for both partners to have a card, since different special bonus earning opportunities are offered by the card depending on spending patterns.

You probably already read this thread, but just in case you didn't -

http://www.flyertalk.com/forum/miles...-chase-cc.html