Ever routed audio a few feet to an outboard effects
processor? How about routing your audio all the way to Oberhausen,

Thanks to the online Tank-FX
(link in German), you can. A server feeds your audio sample into the
tank and records it with a pair of Rode NT-5s, adding a nice, natural
reverb tail of a few seconds, created by the actual acoustics of this
steam locomotive tank. You can then download the result. (via Dave's Imaginary Sound Space, which has an extended discussion)

Of course, thanks to the magic of convolution, you could get the same
effect with a convolution reverb. You can even design your own impulse
responses, which model acoustical reverbs, using the graphic interface
in Impulse Modeler
(US$39.95, Windows) which was just updated this week. For Mac or PC
users with their own convolution reverb of choice, Voxengo has free impulse response files available for download, too!

But it's nice to go organic every now and then.