Sulfur didn't do the trick. Suggestions?
You added sulfur and it didn't work? Seriously? How long did you wait before testing?
It all depends on how acidic you are going for? We have very alkaline soil here and alkaline water too - its limestone heaven! ;) I use mounds of shredded oak leaf mold and pine straw & leaf based compost annually (and I mean BIG mounds) to keep my soil ph in the neutral zone +/- a few tenths.
But if you want really acidic soil then sulfur or iron/ammonium sulfate - given plenty of time to work - is still the best bet as far as I know. Your local county extension office should be able to provide you with info on what works best in your area.
One thing to note about using sulfur to acidify the soil is that it doesn't work as well if it is spread on the surface ass if it is buried. When it is spread on the surface, some of the sulfur is lost to the atmosphere instead of being converted to sulfurous acid (or is it sulfuric acid?).
It takes a lot to make much of a difference, and I think it can take a month or more to start showing effects.
If you're trying to get alkaline soil closer to neutral, I think digdirt's idea is a good one. If you're trying to make the soil acidic for something like blueberries, the only things I know that may help are sulfur and peat moss.
When I planted my blueberries 7 years ago the soil was clay and acidic. Compost amendments have improved the soil to the detriment of the acidity.
We're thinking of starting a blueberry patch. What are the pros and cons of using sulfur vs. peat?