Suggestions for bookshelf speakers that have great dynamics, budget of $500 used.

ELAC?

I had some Haydn Grands and liked them at first, but they were lacking treble (too warm) and kind of boring (not very dynamic) after listening to them for a while.  They are pretty.  I had them in my bedroom, and maybe that was too large of a space for them.  They might be good for a desktop system.  They're the polar opposite of the Monitor Audio sound, so I can see how they might be a good fit if you didn't like that sound.

Greg
Obviously we will see as time goes one.
At this sort of price points it is no big deal if I end up not liking and want to try something else from the excellent suggestions here.
Tbh with my Sanyo receiver with tone controls I can boost the treble a little if needed, I could not really fix the perceived harshness of the Silver’s though when pushed.
I have already found out the Haydn are more critical of placement. I had a little too much bass boom and just moving the LH speaker 3 inch forward and 4 inch further apart and narrowing the toe in cured that entirely.
Oh and they absolutely need the port bungs in place in my application and location.
I certainly am a lot more aware of top shelf monitors around this price now so that is a very good thing indeed!

uber, I found them easy to listen to and if you decide you'd like to try something else, they're easy to move.  I've tried a couple of different Monitor Audio speakers and they were too bright for me also.  Let us know how they work out over time.

Haydn are great looking speakers - since you say they are in good condition, you can resell them at the cost - good thing about getting used gears, as new ones depreciate...enjoy the hunt!