Diners Club gets you one AA mile per dollar. You also get the flexibility of redeeming in other programs if you want, sometimes with BA for double miles. The fee is $80 per year but you can get a 12,000-mile (24,000 DC points) bonus the first year, 1,000 miles for each month with any activity, which more than makes up for the fee. You can reportedly get a "retention bonus" for renewal as well.

If you're concerned with carrying a balance, DC gives you two billing cycles to pay with no finance charges. It's not a revolving charge card, though: you're supposed to pay it off, not carry a balance over time.

Downside: DC isn't accepted everywhere, so you still need another card. IMHO it ought to be MC/Visa since AmEx, including Optima, is also not accepted everywhere (though it's a bit better than DC in that regard).

If you want a Diners, please e-mail me for a referral form or ask any DC cardholder you know. The referrer gets a few thousand miles. You don't lose a thing.