My condolences as well.
tcraft, follow the "Aircraft Registration Forms" link on the site that JAFI linked. There are two forms you need there and a third that isn't there.
The two forms you need (with direct pdf links are):
8050-2 Bill of Sale; and
AFS-750-93 Information in Recording of Aircraft Ownership and Security Documents
The 8050-2 is the document that transfers ownership. The FAS-750-93 has the instructions for filling out the 8050-2. There's a section for how to fill it out and what additional documents you need when the "seller" is an "estate."
The third, that isn't on the site, is the FAA application for registration. The FAA still uses a multi-part NCR form for this (one copy acts as the new temporary registration). You can get this form at any FSDO.
If you need help putting this together, the lawyer who has been helping with the estate (if there is one) should be able to help. If not, a lawyer from the AOPA's legal services panel or an aircraft title company would be a good source. Your local FBO or a pilot friend who has bought airplanes, might also be able to walk you through it.