I am sure that, for many people on this list, these new LED's is quite an old story. Firstly, you can epi-illuminate your SYBR Green stained DNA gels. Background is very dark and DNA bands are seen very clearly. Secondly, you can convert your regular Olympus to a poor man's fluorescent microscope. For example, you can preview cell suspension before feeding it to cytometer.
Background is dark and cells glow very brightly.
For propidium, you may want to try a bluish-green diode. The Home Depot style solutions are particularly welcome.