What monitors sound OK on a bookshelf?

Spendor 3/5 with its sealed woofer would fit the bill!

Omega Super Six Alnico Monitors. I had a pair and then upgraded to the Super 8 XRS Alnico. Louis could build them with the port in the front to suit your needs. Give him a call (203) 847-2800. Custom design,great sound, reasonably priced, and 30 day money back gaurantee.

Joseph Audio Rm7si's

Basic rules are to have a sealed cabinet or at a minimum a front facing port. Other things to look for in reviews are speakers that are mentioned to sound good close to the front wall with a narrow dispersion pattern.

One thought would be Tannoy concentric monitors like the revolution D6.

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.