One thing I have found to be quite valuable for route planning is a local bike map. Sure the Google Bike Maps announced about a year ago are handy. And there are various web sites to help plan routes:
But I really like to sit at the table with a large foldout copy of a map and figure out new routes to try. I have discovered that many communities have bike maps. These will show bike routes, bikes lanes, and bike trails at the very least. You can find them online (usually as PDF files), but I like having a hardcopy. The places I have been have free large hard copies at the local bike shops. If you are searching for one online bike map will tend to find it. They are often combined bike and walk/pedestrian maps. I think that is because that is the way most community budgets work - combining all non-car stuff together.
I have done this with my local Cary map, a Las Vegas map and a San Antonio map. I just pulled up a Nashville map because I am heading there for a few days soon. Which reminds me, I want to try and setup a visit with Walk/Bike Nashville while I am there. Should be at least one good blog post coming if I can set that up.