There are many ways to find good places to paddle. I personally like to explore my area on my own, but you can also get great advice from books and other resources.
On your own: The way I go about it is to go to Google maps and click on the satellite view. Just enter in the name of your town, and click, "Search Maps". This will give you a satellite view of your town. From here, you can locate water ways near you that look interesting. If you double click on the map, Google will center and zoom in. You can click and drag the map around in the window, and I use this to follow rivers and plan my route. I zoom in close enough so that I can see where the boat ramps are. Once you've found a boat ramp, you can figure out how to get there by road, then plan your paddling route from there.
Books: You can always go to the library to look for books on kayaking. Many books will cover techniques, but other books will cover kayaking trips. They will tell you where to put in and what route to take. Of course, this will depend on where you live, so it will be hard for me to recommend specific books for you. So, try this kayak trips, and look for books about trips in your area.
Other Resources: This means searching the web. I prefer Google for my searches. Just type in, "kayak trips" and the name of your town. Other good search terms are, "boat ramps", or "put-ins". I also like to search for "no motor" to find waterways that don't allow motorboats. I'll try to find specific resources for these, and as I find them I'll add them to my blog.