I feel compelled to suggest OP to focus his/her energy on a successful job searching. While credit card rewards are surely tempting, it does not hurt to establish a steady pace and exercise patience -- get started on 1 or 2 good cards (as a new/recent college graduate you probably have only limited credit history) then expand your horizon over time. Study the airline programs (at your leisure) and understand the concept of airline alliance; down the road your job may require you travel therefore you'd have a better idea on which airline(s) would suit you best overall.

OP, I do commend you for thinking of your mother. If she can apply for a credit card on her own let her do that; if not perhaps you can consider adding her as an authorized user on one of your credit cards. However, if your spend on credit cards are limited, you'll want consider the trade-off between a no-fee and fee-based cards for long term usage -- this is, in part, a personal choice so you'd have to determine on your own.

My suggestion is to study the airline programs and airline alliance as stated before. Continental and United Airlines are in a merger and would operate as one airline next year; US airways is a member of Star Alliance (that both Continental and United Airlines belong to).