Under Armor is my current favorite only because its a black mock turtle neck, long sleeve and I wear it under my cycling tops. UA is okay but nothing special.

To touch on the Walmart angle, I agree that you can find products there that as good as name brand. I bought a pair of Starter running socks and realized they were identical to my Nike. I researched and found that Starter is only sold in that store and Nike owns Starter. It is just the Nike low-budget brand.

+1 on Patagonia and I would add REI to that list.

I am very interested in the lightweight wool tops that have been coming out the last two seasons. I personally think wool is the best but hasn't been light enough for me to wear all day.