FBinNY 

As you can see the list is long, and it can be difficult to nearly impossible to identify the cause. There are two approaches -- analysis and elimination,

By analysis, I mean get a sense of the frequency, is once per pedal turn, once per wheel turn, etc. Also, does it happen only while pedaling, only coasting or both, when climbing or sprinting or even at low pedal loads, can you feel it, etc. This will help you compile a short list of likely causes, or at least the likely places to check, cranks, hub, etc.

The other process is elimination, and this is fairly easy. Start with the easiest, remove and replace the pedals with another pair, to rule the pedals in or out, same with the rear wheel, or maybe just the cassette. Try riding standing to see if it might be the saddle or post.

By combining the analysis and elimination methods, you can either find the culprit or whittle the large list of possibilities down to a few likely suspects. At this point you'll probably need to get your hands dirty and do serious mechanical work, which will likely be pointless and frustrating, until you find some stupid cause like the end of the FD cable vibrating and tinging on the seat tube from time to time.