I like to stay at one & a half to two times the inside rim width, so that would be from 28-38mm tires for these rims. There is some fudge room, so you could go down to 25mm, but I wouldn't go any narrower. Here's a link to a chart showing optimum rim/tire combinations (scroll down until you see the red&green chart).

BTW- the oher factor you might consider is your own weight and road conditions. There are many who feel that skinny tires are faster (lower rolling resistance) but that isn't always the case, so if you're fairly heavy, or roads are bad, you may want to stay wider than the minimum.

Here's info about optimizing tire pressure, width and weight.