It is always interesting to hear how things really unfolded years after the fact, when the true stories can be revealed. F-19 was the designation the model companies thought the stealth would be because they skipped it between the F-18 and F-20 programs. The F-117 (if I recal properly, and I may bewrong) was in a designation class usually used for captured Russian aircraft in the US inventory. That way if the designation leaked, it wouldn't arouse much suspicion as a secret program.
I have also heard that the codename Aurora was actually used for the B-2 program before it became public. So really all of that mysterious work the Air Force was doing on that super secret "hypersonic reconessance aircraft" was probably just preliminary B-2 work. On the topic of secret spy planes though... anyone who keeps up with Aviation Week magazine had probably heard about the new stealth recon UAV that was used over Iraq. No official anouncements yet, but the AF did acknowledge that it exist. Rumor has it that it is a derivative of the Dark Star UAV built by the Skunk Works.