Just a quick plug for an excellent product I found a few months ago and have been using ever since
Qbrew is a free-source homebrewer’s recipe calculator which you can download and use to formulate recipes. Basically, you can put in the quantities of malt (or extract) and hops you’re using, set your “efficiency” (i.e. how good you are at turning raw ingredients into alcohol) and end up with predictions as to the colour, bitterness and strength of your beer. There are a load of recipe “styles” you can compare your beer too and there’s even a handy hydrometer correction tool.
How do you work out your efficiency? Well, if you have a few brews behind you, you can put in the raw ingredients and play with the setting until you get Qbrew to end up with your end product.
Once you can get over the disappointment of being told you are only 60% efficient, it’s an extremely useful way to predict future brews. [Various snotty homebrew books say that “beginners should achive around 80% efficiency”! I blame London tap water]
I’m fairly new to homebrewing, so was surprised to find that there are a number of homebrewing programmes out there – though most of them you seem to have to pay for, and I’m not sure if the added features are worth it (“Hop Time Degradation” calculator, anyone?)