What are optimal fabrics for cycling clothing? The title says it all. 

However, should I vary the fabric through the year? Should I go with lycra in the summer and wool in the winter? And maybe, should I wear cotton?

I do 2 types of riding. Commuting and endurance cycling. 

There are optimal fabrics for cycling and for athletic gear in general. What should I look for regarding cycling clothing?  

October - April = Typically wet and cool/cold. We don't get much frigid weather, but it does occur for short periods. 

May - September = Usually warm and dry. We don't get a lot 90+F temps, but do at times. Out on the coast it can be cool and damp this time of year. East of the Cascades, hot to very hot and dry. 

Can this be converted to a community wiki? It has become apparent that the optimal fabric is personal choice and climate determined. Personally, I prefer merino wool and lycra/synthetics; but others find cotton to be their optimal choice.
Wool, particularly Merino wool, is tough to beat. It's partially hydrophilic, cooling you by wicking sweat away from the skin while also retaining warmth when wet. It's lightweight, soft, and has natural mild antibacterial and antifungal properties that reduce the amount of funky odors.

The main downside compared to synthetic fabrics is probably cost, especially for cycling-specific apparel.