I always just tune to Flight Watch on 122.0 and they can give you just about any type of specific weather information you request. Keep in mind though that they close at night after 10 PM, so you'll have to contact the FSS for enroute weather during night hours.
Flight watch is also where any pilot reports you make should go.
I know that whenever I fly, I try to give a pilot report for each and every leg that I fly. I sometimes check on DUAT to see if the PIREP has been published, and most of the time (9 out of 10) it is.
Often times, that unforecast weather isn't published with the PIREPS, but it is passed on to other aircraft in the vicinity. An example of this would been when you're flying in and around thunderstorms and turbulence. The controllers will often tell you what an aircraft 10 miles ahead of you is experiencing, and what you can expect!!