Koolstop Salmons are the next best thing to switching to discs.

As has been noted, they work well wet or dry though they wear a little fast.

Personally I have pretty good luck with Nashbar's replacable pad shoes, they work OK when wet, perhaps not quite as well as Koolstop salmons. I switched to disc primarily due to ice buildup in the winter which not even koolstops will fix.

I think the Nashbars are pretty much identical to the low end Shimano shoes. I buy new pads when they go on sale.