I've been making fictional ballparks with the Ballpark Creator posted in this thread:
http://www.ootpdevelopments.com/boar...generator.html. Then I resize them and stretch them out a bit and add a little background, usually a city skyline and some logos.
The nice thing about them is that I can make and update them relatively easily. For example, I've made stadiums for all the teams in the PCBL and can update them each season to add championship banners, retired numbers, change logos, or whatever.
Here's an example:
The Swamp
