During training on the FACS machine in our faculty facility, I encountered the Fluorescence Spectrum Viewer from BD bioscience.
It is a JAVA interactive site that allows to to view excitation/emission spectra of up to 8 differnt fluorophores simultaneousely.
It lets the user to choose the desired excitation laser, and shows the excitation & emission spectra *to that laser*. moving the cursor over the spectra gives you actual numbers of % excitation & % emission efficiency.
You can use filters to test which filter is most suitable for your fluorophores.
This site is intended for FACS users, so you can choose from any one of a number of cytometers from BD. However, I think this site can be usefull for microscopists too.
EDIT: I found more sites like that, each with its own set of fluorephores –
Fluorescence SpectraViewer at Invitrogen (Life technologies) site.
Fluorescent Dye Spectra at U Arizona (only chemical fluorophores)
Evrogen Spectra Viewer at Evrogen (only a very limited list of fluorescent proteins)
There is also this Cell staining tool from invitrogen. The concept is cool, but I think it is a very limited tool and I don’t think it is very helpful.