I've been working on this for awhile, and finally got it all together - a set of photographs on flickr that serve as a virtual tour of my library.
It is a fairly simple approach to a virtual tour, in that I just took pictures of all the different areas of our library, wrote up little descriptions of each area, and then linked them together using flickr's notes feature (I also made a floor plan of both levels and linked all the areas that way, too). It makes for almost a self-guided tour of the library, and someone who saw it recently said it was like moving through a video game or a "choose your own adventure" story.
It's a little less fancy than other tours out there, but I liked it in that all it really required was time - no special software or skills necessary (other than flickr, obviously). Also, being flickr, patrons can leave comments, and the photographs can be easily repurposed for other uses.