Here's a little secret: If you book directly on United's website enough, they'll give you money back after you've booked a few flights - even if it's for someone else.
Clearly, this is going to benefit people that actually fly a lot or act as booking guru for family members and friends. United TravelBank will give you a credit for every flight that you book directly on the website. It originally started as a stayover from Continental's own program. Though it's not free, it's cheap enough that, well, even I'd consider it. Only I don't fly United enough.
To enroll in United's TravelBank, you have to pay an annual fee of $25. Every time you book a flight - for yourself or the missus - you get a credit of $5. (To get the credit for someone else, you have to be logged into your account when you make the purchase.) There seems to be no restrictions on whether it is a one-way trip or round-trip. You have to book five times to break even, but every flight after that will net you $5. You don't have to be a genius mathematician to figure it out, but you do have to know your own travel habits.
You have to be a MileagePlus member in order to take advantage of the deal (that's free, by the way), and the credit is then issued into your United account that you have to use, well, at least before the decade expires. The terms and conditions give you at least a year or two, c'mon, it's probably not that hard to use them.
