I prefer the WI eccentric hub in a SS application w vertical drops over a fixed wheel application. If you have the money it's handsdown the best alternative to a vertical dropped frame if you must run SS.

You can also try an eccentric bottom bracket. I believe Bushnell makes one for standard BB's now, but I may be mistaken, and it's more expensive than the WI hub.

Or you could go all out and run a ghost ring: