The only bookshelf I use speakers on is in my living room. The speakers are part of the JVC EX-A1 I use there.
The speakers are tiny - H, W, D are - 4 3/4" x 6 3/8" 9 7/16". They barely clear the smallest shelf on the old teak shelving unit. Speakers as large as 9 inch H could fit, but for the location and use the stock speakers are fine.
The wood cone speakers do a decent job with FM and light CD work. I don't like them for any real listening. Interestingly the receiver portion is excellent and I have used it with much larger speakers in the past.