Hi,
avoiding workflow software with an integrated imposition software, I think you have many opportunities on the market of stand alone applications.
Recently I had the same need and I did a research and several demo. If it could help, here my opinions:
PREPS (by Kodak): expensive, robust, complicated but very powerful imposition software (it's the one I choose at the end of all). It may handle every kind of most perverse imposition you can remotely imagine. Last release (should be n°7) isn't bug free, but it works great. Some steps are not so intuitive. Better to invest in some training, just to avoid any sort of problem.
IMPOSITION STUDIO PRO (by Devalipi): cheap, flexible and a great piece of software. However is limited in capabilities that go out of a certain standard. Devalipi provide a great customer support, but sometimes they don't have a precise idea of I was speaking about (especially in ganging different jobs together)
ImpO2 (dy Dynagram): I loved it a lot, it's a plug in of Acrobat, in the full optional license has many features that are useful. It also provide automation, wizards and "on the fly imposition" for quick jobs. It cost as a PREPS license, and like preps, it is not so intuitive. Unfortunaltely, I am still waiting for a reply about having some training.
This software is very similar to QUITE IMPOSE. (If they would had reply me, probably would have been my choice)
DYNASTRIP (by Dynagram): alter ego of Preps, don't know if it's developed, the softhouse is pushing ImpO2 over the market
IMPOSTRIP (by Ultimate): Impressive software, it comes out in so many ways, with so many modules, with so much features that leaved me confused. Had a demo of it (they go from plug in for acrobat for the basic impositions to a complete client/server automated solution), I was very impressed by it. However I still waiting that the tech guy find some time to show me what I really need (they show me a fantastic show of what they can do, but when I asked something the answer was always one: got no time for this yet, we talk about it later. No time… ok, no customer)
PUZZLEFLOW ORGANIZER (by Puzzleflow): on the paper seems fantastic, I'm still waiting for any answer…
METRIX (by EFI): just a word, AMAZING! But the most expansive software that I ever looked at.
But the main question youhave to answer to yourself is: what kind of impostions (jobs) I have to handle?
From that answer, it will be easy to focus on the right product.
Good luck!