Is there a list of a few professional websites using smugmug that we can view before starting a trial?
A great option I like to use is the search function on www.smugmug.com. Enter a keyword in the search (upper right), for example, wedding, portrait, landscape, etc., for a topic you are interested in, and applicable photos will be displayed in the search results. This is a great way to look for and view other SmugMug sites. You'll see both professional and non-professional photographer results in that search.
Below are a few specific examples as well: