The Morphing Mushroom Identifier (MMI) at MycoKey is quite a good on-line resource for keying out all kinds of mushrooms. It’s not complete, but still very usable. (Apparently the full version costs extra and is installed on your own computer.) You start by choosing the gross body shape and hymenial structure (i.e. gills/pores/teeth), and narrow it down further by selecting all sorts of other parameters like color, cap shape, size, staining, etc. I tried a few types I know, with good results.
This tool does not give you the exact species, but it is very capable of keying out the genus, or sometimes two or three similar genera, thus permitting rapid consultation of Mushroom Expert or your favorite guidebook for more detailed identification. This would be an especially good resource for novices to try. However, it also may be of use for more experienced collectors keying out unfamiliar or confusing types. If you have a microscope, it even lets you specify size, shape, and other details of the spores. Worth bookmarking! I’ll add it to the permanent resource menu.