Microplace sent a really interesting offer to my inbox: lend money to the world's poor, hardworking micro-entrepreneurs, at a modest profit - but take your money out when you need it!
Microplace, run by Calvert's socially responsible financial services along with Ebay, has been offering this opportunity to be a mini-microlender for about a year, but this is the first time I've seen the option to do so without locking your money in for a specified time period. I think this is a neat way to stash short-term funds, knowing they're being used by women to help climb out of poverty. (Note that it's still better to invest for a longer time period, so the Microfinance Institutions don't constantly need to chase capital.) If you don't know when you'll next need a sum which can safely put away for awhile, this is perfect.
Generally at Microplace you designate your desired interest rate and chosen time frame. (This is different than Kiva, which pays no interest, though the borrowers do, of course.) To take advantage of this offer, you need to specify "Repayment Anytime".