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The observation of ultra-high energy (UHE) cosmic rays (E>10^18 eV) is one of the most intriguing enigmas of physics at the start of the new Millennium. The reported detection of cosmic rays above the Greisen-Zatsepin-K'uzmin cut-off (at ~6x10^19 eV) only deepens the mystery. One of the most powerful techniques for investigating UHE cosmic rays is the fluorescence detector. The Fly's Eye experiment at University of Utah was the first to successfully deploy this technique to observe air showers. The High Resolution Fly's Eye Experiment (HiRes) extends the aperture of the original experiment by another factor of ten. HiRes is now fully operational and will run for the at least the next five years. Experiments are now under construction and being proposed to extend the aperture by additional factors of 10-100 beyond HiRes.