many discussions have been posted on this topic and you can do a search on the past topics in this forum.
You can also visit gleff's or pgary's websites to see excellent summary on that. basically, the starwood amex is still a good card given your expenditure. Besides the aforementioned United card, there is a promotion on Delta amex with 15000-17500 bonus miles which is free for the first year. There was a Northwest visa card first year free with 15000 signup miles but offer expired last month. You can always expect to see new offers like that from different airlines.