From the WIKI:
.Filterable fields you’ll notice things like title: and type: and you might be looking for the other fields you can use to filter your collection. The various fields can be found by opening your library, setting it to table view (click on “view” to alternate views) and right clicking on the columns’ headers. Most of these fields can be used to filter your collection. Some are not exact matches. For instance to filter by My Tags you must use mytags:. Below is a list of the fields and their corresponding search format. Image – Not usable Type – type: Title – title: Author – author: My Tags – mytag: Rating – rating: Abbreviated Title – abbrev: Alternate Title – alttitle: Tags – tag: Electronic Publication Date – epubdate: Languages – lang: Publication Date – pubdate: Publisher – publisher: Series – series: Subjects – subject:.
--Collections
I suggest a drop down list in the "start with" box in the collections tool.