Looking at the Star Silver and Star Gold charts and the mileage expiry thread, the best bet(s) are:

Air Canada - 12 month expiry if no activity up to a max of 7 years (7 more with a free), Credit Card points via SPG
Asiana - 5 year expiry (7 if elite), Credit Card points via SPG, easy to earn Star Gold, lifetime status at 1MM on *A
BMI - no expiry if activity every 2 years, fairly easy to earn Star Gold, no way to get credit card points, will end soon.

American Express and Diners Club both will let you transfer into SPG. SPG has a number of airlines that you can transfer into.