Where can I find baseball uniform information?

The best site for baseball uniform information is Dressed to the Nines at the Baseball Hall of Fame's website: http://exhibits.baseballhalloffame.org/dressed_to_the_nines

You'll find a database of major league uniforms, as well as patches/memorial markers and retired numbers.

For players' uniform numbers, Baseball-Reference lists players' numbers, and include numbers by team/year as well.

For up-to the minute uniform commentary, read Uni-watch.