Google Patent Search - https://www.google.com/?tbm=pts
USPTO - http://patft.uspto.gov/netahtml/PTO/
Freepatentsonlne.com http://www.freepatentsonline.com/search.html.
The Patent Information Users provides a list and brief overview of many patent resources. http://www.piug.org/vendors
The USPTO has a report with a list of top 50 patent holders for selected years: Ranked List of Organizations with 50 or More Patents Granted During the Period, as Distributed Either or Both by the Year of Patent Grant and by the Year Of Patent Application Granted: 01/01/1994 - 12/31/2013 http://www.uspto.gov/web/offices/ac/ido/oeip/taf/meddev.htm
The FDA has several databases http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/DeviceApprova