You could apply for the Starwood Preferred Guest card from AMEX. Earn 1 Starpoint per $1 charged. When transferring 20,000 miles, Starwood adds 5,000 for you. Points transfer 1:1 into miles for Thai Airwars, SQ KrisFlyer, (and many others) but unfortunately 2:1 for United MileagePlus - don't know why. Read comments on other credit card threads - people are generally pretty happy with this card. First year free, $30/year after that, but has some nice AMEX perks.
View airline conversion rates here
-minimum is 2500 points:miles conversion, 1500 for SPG gold/plat members

On a side note, has anyone experienced any difficulity redeeming one star alliance members miles for another's award ticket - i.e. United Miles on Thai Airways? I know the mileage amounts are the same regardless of airline, but wondered if it was any different. That way,I could transfer Starpoints into TG Miles, then redeem on United (for Domestic tix, of course). Thanks in advance.

There is always also the United MileagePlus Visa Signature - $60 annual fee, earns 1 UMP mile/$1 spent, double miles on United purchases, etc. Currently there is a promo for new accounts that gives 20,000 miles upon approval - this card is also discussed in its appropriate credit card thread.