This has come up a couple times and I am in a very similar situation. I have an awful setup to my room and have the speakers sitting on top of the bookshelves and have shims underneath the backs to angle them down. This is for a couple reasons. First, most bookshelf speakers are deeper today than they were 20 years ago when I bought my Infinity's. 8" deep speakers were more common then. Now, my Revel's are 14" deep and won't sit on a bookshelf. I get several extra inches of space by placing them on top. Because I am so close to the wall, I also use the port bugs that ship with them which are just cylindrical pieces of foam you stick in the port to reduce reverb from the wall. This was the best possible setup for me.

Otherwise, you need to find speakers that are really small or approximately no deeper than 8" if you have a normal 10" bookshelf to give you room to run the wires. One other option would be to do a wall mount, which can work out quite nicely. Those were the two options I was looking at until I decided to put the speakers on top of my bookshelves which is not ideal, but still better than jamming something into the bookshelf that doesn't fit.

My first question is what are you going to be powering the speakers with or are you choosing the speakers first?

If you have to put them physically on the shelf, you might want to look at the "SAT" type speakers. From most audiophile companies, this is going to be about a 6" x 8" x 8" speaker. A few speakers worth demoing

PSB Imagine Mini - $829 - SAT Type Speaker - Crutchfield and Audio Advisor
B&W M-1 $499 - SAT Type Speaker that is one of the rare B&W products I would define as a value. These easily could be $200 more and would be fairly priced. Best Buy
Focal Chorus 706 - Front ported but a bit on the large side
Focal Chorus 705 - Front ported and smaller
Focal Chorus 807 - Front ported but a bit on the large side
Focal Chorus 806 - Front ported and a bit smaller
Just contact Music Direct - they seem to always have deals on Focal Speakers for pricing but these are all between $549 and $899 I think.
Peachtree Audio D4 - $699 - Very inefficient at 84dB, but sound awesome. Must use port bung
Peachtree Audio D5 - $999 -Might be too big to fit on a shelf and again will need port bungs - Crutchfield & Needle Doctor
Polk LSi M 703 - $749 - unported but very big - Crutchfield
Dali Mentor Menuet - $1599 - Dali specifically says this speaker is designed to work in a bookshelf and gets a 5 star rating from WhatHifi - available from Needledcotor
Rega RS1 - $799 - Rega claims that despite the rear port, these can be placed on a bookshelf. Needledoctor & Audio Advisor

I would get out and listen to as many of these as you can in stores - narrow it to a few you like and then but from a place with a liberal return policy like the four on-line retailers - Needledoctor, Music Direct, Audio Advisor or Crutchfield. They all have 30 - 60 day return policies.

If you can put the speakers on top of your bookshelves, then the list might change a bit as I would look at more traditional speakers.

Any of them. I haven't heard anything better at any price. You'd have to spend much more for bass extension. In which case I'd recommend Chorus floorstanding. Or pre-kevlar B&W if you don't mind vintage.

The only thing I would advise for a bookshelf placement is a truly sealed speaker with no ports. This is the only way to get good performance IMO.

The NHT Classic Model Two is an excellent one, and they run $329 each at Audio Advisor. Strongly recommended.

Bookshelf speakers rarely provide what I would deem full sound in a 2.0 system as opposed to a 2.1 system. Especially speakers that are going to be sealed which is what is going to work best in your environment.

I personally, like to see a speaker get below 40hz if I am listening to rock music and deeper for classical before I would consider that full range. This is largely because a bass guitar, properly tuned will play to about 41hz. If you listen to piano centric music, you need to go deeper as a piano will play as low as 27.5hz. Pipe organs will go to 16hz but I don't think many folks are concerned with that.

Of the speakers mentioned, the Focal 706s are rated to 47hz and the 807s and the Polk LSis are rated to 50hz. Those are your best options for the fullest sound if you are vehemently opposed to a subwoofer. If commsysman is right, and he often is, that would mean the Focal's still might be a problem given the front port.

I personally have subwoofers paired with all 4 sets of bookshelf speakers that I own. However, the best bass performance I get out of any of them is 60hz with my Revel Performa3 M105s. But, in all cases I entered into my purchase certain I was going to add a subwoofer and as a result, was not ultra focused on bass performance.

It really goes without saying that the low bass performance of ANY bookshelf speaker is going to be limited.

Some people find that this is not an issue for the type of listening they do, especially if their speakers can go down to 50 Hz or so.

But if you want a lot of low bass, you either need some large floorstanding speakers with 10 inch or larger drivers, or a subwoofer.