I might be able to help you with your search for your "family crest", however I think there a few things that you should know.
First and most importantly is that there is no such thing as a "family crest" or any such nonsense like that. What happens in this case coats of arms have been so romanticized over the centuries that everyone wants one. There are countless companies that prey on unsuspecting and unknowing consumers. The truth of the matter is that coats of arms are registered to specific individuals. These people pass, hereditarily, coats of arms to thier children...but the arms that are inherited by the offspring are "differenced". For more information on coats of arms (whose technical term is "armorial bearings"), consult a few books and/or the College of Arms of England. A good reference book for begginers is "The Complete Guide to Heraldry" by Fox-Davies. A used copy can be obtained online for literally about $10 or so, and it is an invaluable resource.
As far as identifying which arms belonged to your ancestors, you first have to know which part of which country they lived in. English records are the easiest to find, but coats of arms existed in almost all of europe and even as far east as Russia. In England, the records that need to be consulted are called "Herald's Visitations". The title would usually be something like: The Herald's Visitation of Oxfordshire in 1589, 1612 & 1632 (for example). There are also other sources to consult as well including; period Rolls of Arms, Grants of Arms, and Armorials. Many of the Rolls of Arms can be found in a wide variety of places, and so can many of the Armorials (which are a collection of arms, usually from a specific general location). If you have the patience (and the money!) you can pay the governmental body responsible for Armorial Bearings in the country of your Ancestor to research your ancestors specifically, but this is usually slow and usually costs a more-than-meager amount of money.
I do have some access to some of these records and, depending on which country (and county) your people came from, I might be able to help out. -John Clayborn