Does anyone have or know of a list of fxFiles and pictures of them?
There's been suggestions of doing an index like that over at the Map-Review forums. Poke Tito and business_eskimo enough and they might do it. (They put together the awesome md3 model index with thumbnails that we host on MR.) But until then, your best bet is to either try an effect out in-game, or unpack it from the pk3 and load it up in EffectsEd.