I also got the trekking bars from Nashbar and put them on my touring bike, just like George's picture (but using gripshift). I'd think any regular mtb brake levers would be fine -I didn't try putting the levers farthest away from me as I felt I'd just be too stretched out; if I put a shorter stem on to compensate, I then felt like the bars closest to me made me feel like I was cycling with my arms pointing too much of an acute angle down and almost towards me. Anyway, after messing around with the angle, using a couple of different stems, I just couldn't get on with them and relegated them to my backup tourer/commuter bike.
Strange this is, as soon as I put them on my backup bike, they felt much better. I think the problem with the trekking bars is that they are perhaps more sensitive to setup and require just the right stem length and appropriate rise for the given frame.