Got a brother who is moving to Rockville, Maryland this May.  Need recommendations on where to fish when I visit him.

http://www.dnr.state.md.us/fisheries/recreational/fwhot.html

There's a few lakes that aren't too far from Rockville you can hit. Just to give you an idea, Black Hills regional park (Little Seneca Creek lake) in Germantown is hitting the spawn about the beginning of May. The link that dsaavedra posted will help you out too!