If you don't have the flexibility to manipulate your spending (say, frontload your insurance premiums for the year, or income/property taxes), there's not a whole lot of opportunity. Compared to before, there are not many cards out there that don't have a spend requirement for bonuses.
if you write a rent check to somebody, you could probably utilize RadPad and come out ahead.
Some peopel get tempted to spend more to hit these sign up bonuses, so if you are a naturaly low spender and don't have the cash to frontload expenditures on paper, I would just pick the card that gives you the highest amount of cashback in the category that you spend the most in, OR something with a signup bonus that you know you can hit.
See fatwallet.com/forums/finance/711457