I've always ridden in pure merino tops for quite a while now, but after the thread on here a few days ago I thought I'd try one of the merino-synthetic hybrids.
Just got back from my first ride in a Helly Hansen Warm Freeze top, which I picked up on Amazon for just £25 (thanks to whoever it was that posted a link to those!). Very impressed. All the warmth, comfort and stink-resistance of merino, but wicks and dries much faster.
The black HH tops are still under half price on Amazon, for those that are interested (link). Well worth it at that price, IMO.