My plain t-shirts come from Lands End. Nice quality, well made.
The majority of my t-shirts have some kind of print on them. Most are from Hawaii, whether it's from a luau, restaurant, or just something that is a Hawaiian type of print, but I also have t-shirts from various national parks, a couple that have "witty" sayings on them, etc.
It's rare that I wear a plain t-shirt out in public...