I'm using Kiva, and find it quite good. It is very easy to get started and therefore probably a good microfinance institute for which to give a gift voucher. The recipient can just log in and search for a type of loan they like (carpenter, bakery, motorcycle transport etc) on a continent of interest. You get the $25 back after some months and then you can re-lend it to some one else, or you can have it paid out to your paypal account. Easy.
Of course, to be a responsible lender you need to use your head a little and read the information provided. Loans from different continents often have different conditions, and you should make sure you know what your money is spent on. It is now more common with backfill loans, that is, the money raised through Kiva is used to cover a loan all ready made to the borrower(s). This is usually stated on the borrower's info page and as with any financial transaction, you should check up on the details. You probably want to read up on the micro-finance institutes that distribute the loans you are interested in (compare interest rates and the risk of you not getting your money back). There are a lot of groups of borrowers on Kiva nowadays, and there are some quirks to this: each group member may use his/her share for a different purpose, the group usually will have to cover members not paying back and the repaying time is often much longer than for smaller individual loans. Also unless you want to make a donation to Kiva in the process of lending your $25, make sure to select that you want to donate $0.00 to Kiva (not this time)! They have recently changed this, so the default is to donate an amount.
As pointed out in the article in the second post, there are no guarantees that the loan will be used as advertised, something which might be worth to keep in mind if you have strong views on how your contribution should be used.
They say the grass is greener on the other side
-- but have you ever flipped it over?
The Jean-Paul Sartre cookbook: "Today I made a Black Forest cake out of five pounds of cherries and a live beaver, challenging the very definition of the word cake."