I've been on Kiva for about 3 years now. One of the things I like the most about microlending is that I feel like I get a lot more effect for my dollar. When it is repaid I can lend the same money over and over and keep doing good without breaking my own bank too badly.
I found an easy way to build up a little stash for lending for myself was to tie it to my rent. Each month when I paid my rent, I decided to help someone else earn theirs. I would make a $25 loan each month until I had a little pool of $500 that I could keep circulating. Now I don't add anymore money but am still able to lend regularly. I've never lost a dime in default.
This way you don't have to be a fat cat to feel like you can keep giving on a continuing basis.