I am currently in a small library. We have limited space. The only displays that we have aren't even really displays. We keep the new books wrapped around the side of the circulation desk. This does attract a lot of attention. I really wish that we had more room to do displays since they seem to be the most beneficial for reader's advisory. We have books set up here and there, but not enough room anywhere to do anything themed. We do a few spotlights and some pairings.
If we had room to do displays, that would be my biggest choice. I would do them based around a certain theme. It could be genre, it could be topic, it could be character-related, it could be what the staff are reading. There are so many options available when it comes to displays. You are able to change them as frequently as you like and hit different things with each one. It allows for a lot of versatility.
We have started doing some lists, but there is the space issue there as well. We keep a best-sellers list and have posted some read-alikes for popular authors. I feel like annotated lists would be a better bet since it allows the reader to get an idea of what the book is about. There you have to compromise space, though. You can't fit as many books on an annotated list as you can on a read-alike one.
We have tried bookmarks, but they don't really seem to be a hit with our patrons. It is something that they just gloss over at the circulation desk. It is probably because we always have bookmarks setting out.
In a perfect set up, there would be ample room for displays.
As far as online goes, we do have a Facebook page and a Goodreads account. Through Facebook, we share the new titles available. Through Goodreads, we provide different bookshelves based upon genre and other topics. If we had a bigger online following, this would be much more helpful. Unfortunately, our online presence doesn't get as much traffic as we would like. The majority of our patrons fall into the senior citizen age range and tend to be less likely to check online resources. For a different community, though, this could be a good way to get reader's advisory out there.