In reply to Little Billy:
I have assorted merino tops and really like them all. Other manufacturers are:
Smartwool
Embers
Finisterre
Howies
Chocolate Fish
If you're quick, Howies are doing a 20% discount on everything with the discount SPEEDBOAT. Depending on your size, Embers have a few things on sale at good prices, but do watch out for their sizing, as I've found I need to go for a size up from my usual size.
One significant benefit of merino over artificial fibres is that it doesn't get as whiffy after a few days, and I do find they feel nicer.