Ask Mr. Smarty Plants

That's a really tough question because: 

1)  You didn't say where you digging.  Was it in the woods?  in a flower bed? in your lawn?

2)  Did the bulbs have any other living plant material with them?  a stem?  leaves?

3)  What size were they?  an inch in diameter?  half an inch?

The toughest part of the question is, however, that even if you had provided these facts, there really isn't a database for identifying bulbs.  Also, there are several bulb-like structures—corms, tubers, tuberous roots, rhizomes—that are confused with true "bulbs".  Many plants in the Family Liliaceae (Lily Family), Family Iridaceae (Iris Family) and Family Orchidaceae (Orchid family) have bulbs, but there are many other plant families that have bulbs as well so there isn't really a good place to start a search for what type of bulbs they might be.  Here are the plant families that the Pacific Bulb Society lists as having bulbs.  You can see by their page "What is a Bulb" that their definition is not as strict as the one given above.

If the bulbs you dug up were in a flower bed or a lawn, they are very likely a bulb from a non-native plant and, since our focus and expertise are with plants native to North America, we aren't like to be much help in identifying them.

If you found them in the woods or where other native plants grow naturally, it is more likely that they are the bulbs from native plants.  If you normally visit the area, do you remember seeing plants growing where you were digging?  That would give you a clue as to what they are.

Either way, your best bet to find out what they are is to either plant the bulbs you dug out and see what grows from them or watch the area where you dug them to see what sort of plants show up there.  When you have a plant to associate with the bulbs, take a photo of it (wait for it to bloom, if possible), then visit our Plant Identification page to find links to several plant identification forums that accept photos of plants for identification.  You could try submitting a photo of the bulbs you found to one of these forums, but I think it is very unlikely that anyone could identify them.