These are my favorites so far this year for espresso.
I got them from our Walter (Kaffeespezialitaet.at).
The Ruanda is a very sweet SO with nice but not overwhelming acidity. I find it quite forgiving. It reminds me of the nice Yemen Mattari but I find it cleaner.
The Trabocca Yrg is the best Ethiopean I've ever tried. (Not that I've tried too many, maybe 10 or so.) It's a bit more sensitive to change of parameters but at low doses I get very nice fruitiness and sweetness (sweet orange or tangerine).
I think jamesgourmetcoffee has both these beans as well.