If you're talking about staining developers, I'll put in a plug for Pyrocat HD - it's also a two part liquid. Bostick & Sullivan ships part A dehydrated, but you just add warm water to reconstitute it and you're in business. It too lasts a very long time in stock form - I've had a bottle of stock that's lasted a year. Diluted and combined to working strength, you're on the clock to the tune of an hour or so before it starts to oxidize, but that's true with most of the staining developers. They're great for contrast control, as the stain serves as a contrast mask and helps keep highlights under control.