If you are looking for an all-purpose merino longsleeve base layer, I love the Smartwool microweight crewnecks:
http://www.teamestrogen.com/products.asp?pID=19348
I find these particular SW shirts run a bit large- I usually take a medium in everything, but in these I need a small. The SW microweight is a tiny bit thicker than the Ibex "woolies" thin baselayer. The Ibex are longer torso too, so you may have to tuck them in. The SW crews are more "normal" length and can be worn as an outer top alone too. They are not "tight" or too fitted. (NOT fitted at the waist like the SW Zip-T's are.) The Ibex woolies have more of a long-john look- with long cuffs, long torso, and a snug fit. Both are nice, but the SW crews are more versatile for various uses.