If you're using dry yeast, you can just reconstitute it as per the directions and pitch. I believe one 11 gram packet has the recommended cell counts for a five gallon batch, but someone might want to elaborate on that.
Liquid yeast, such as Wyeast and White Labs, pretty much require a starter. A stir plate is almost a requirement as well. A 1 liter with stir plate will get the cell counts you need. A 2 liter starter -- shaken -- might be just enough.