bookshelf speakers

I know that bookshelf speakers are not meant to be actually placed in a bookshelf, but I can I do? I only have room for a pair in a long bookshelf. It is actually more a ear level (sitting) bar with some books on it. No room for stands. I would like some help from you guys to shortlist a few speakers that would serve my needs. Again, the place for the speakers is a shelf about 50cm wide and therefore there is some room for a placement away from the wall. There are not other shelves on top of it. All suggestions are welcome. At this point I still don't have an expected budget, which I will define as soon as I have shortlisted the speakers.

Thanks for your help.
No budget, no ancillary equipment, no musical styles given....... Some very general rules for bookshelf speakers actually placed iin a bookshelf:

sealed cabinets are good, no ports to deal with

if the speaker is ported then of course they must be front ports.

Focal comes to mind for decent monitors with front ports.
Daber Audio speakers. I have the Monitor 3's they are excellent IMO. Under radar American made brand. Also like PSB speakers pending budget. Happy hunting alot to out there.
You should be OK as long as are not putting the speakers on shelves inside of a bookcase, because then you would be putting a box inside a box. Up front realize that the speakers can be made to sound very good, but not their very best.

Sealed speakers or front ported speakers will work better than rear ported speakers, though some rear ported speakers will surprise you with how good they can sound on shelves Rega RS 1 .

Placing speakers vertically, as opposed to on their sides, works better unless the speakers are designed to also work on their sides, like the Ascend Acoustic Sierra 1 Monitors .

Speakers that I have owned that worked very well on shelves: Ascend Acoustic Sierra 1, Rega Ara (now the RS1), NHT SB2 (now the Classic 3). Speakers that did not work very well on shelves: Totem Mites, Energy RC10, Wharfedale Diamond 9.1 (now the 10.1), B&W 302, EPOS ELS3.

I have the same constraints. I have Von Schweikert VR-1 speakers sitting in bookshelves. They are amazing. Very surprising. One might think the sound would be severely compromised but, in fact, it is holographic. The speakers disappear. The only thing lacking is extreme depth but there is depth, height and width. Voices and acoustic instruments are very real. I added a small closed REL sub which crosses over at 50 Hz. It adds a lot to the realism.
There are a couple speakers called the'Clue' and 'Guru', that are made for close to a wall and not sound bass heavy. I just can't think of the builder right now. There are others but, I don't recall them.
Clue is by Sjon or something very similar. Very very nice when set up close to the wall.
I totally agree with Rar1 that RegaRS1 sound just fine in a bookshelf, R1 even better, used them for years in bookshelf and I'm picky about my sound.
Speakers without boxes would be the best choice. And probably the best of that design would be the Gallo Stradas. Their imaging is spooky good and they have several mounting configurations, including a very nice table-top stand...

Also consider Salk WOW 1 mini-monitor, a well built speaker that can sit on a bookshelf.
NHT Classic 3. Small, dense, 3way, inexpensive these days. well built and sound great.
The Wilson Duette's are specifically made to be placed right up against a rear wall / housed in a cabinet or on a bookshelf. If in the future you want to move them out into the room, all you have to do is change the supplied external resister and change over to the supplied grey cable versus the tan cable and you're set to go.
How deep are the shelves? I'd say either the Silverline Minuets for something on the shallow side and Silverline Minuet Supreme Plus is you have the space.

The little Minuets sound very good on shelves and play well with a broad range of equipment.
I went to a guys house who had Joseph Audio RM7 XL's actually in a bookshelf. Surrounded by...books. He was driving them with Simaudio gear and they sounded great to me. I'm not the most critical listener but I thought they sounded great.