In my experience, Silverline Minuets are worth a look. They're rear-ported but are largely indifferent to placement and can benefit from rear-wall reinforcement. A couple of others monitors that are frequently recommended for use in a bookshelf are Rega R1 or RS1 and Von Schweikert VR-1. I haven't heard either, but many people swear by them for this application. Some sealed or front-ported models are tricky because they're designed to be used in free space. The question comes up pretty often; a search on the topic would give you additional ideas.
What monitors sound OK on a bookshelf?
I bought a new house with a living room that has beautiful bookshelves and layout complications which restrict my ability to use stand mounted monitors for the front channels. I want to buy some small speakers that will sound OK sitting at ear level in the bookshelves. I love Harbeths, for example, but have no idea how they would sound in this setting. Any thoughts on good options?