I will avoid trotting out all the names you're likely to have come across already - and perhaps focus on some of the smaller (but high calibre) firms that you may not have come across. I'd take a look at the following (and apologies to those firms I'm inevitably going to forget to mention, this list is just a starting point - so do add further details to this thread!)
Cairneagle - a strategy and venturing company whose leadership are ex-LEK, Roland Berger Strategy Consultants, etc.
Cairnforth
Candesic - put together by former McKinsey consultants so has a proper strategy consulting pedigree.
Credo - "Credo is a Strategy Consulting firm with a reputation as an agile and highly effective alternative to the traditional consultancies."
Edengene - a strategy consultancy that works with large organisations to drive growth.
... hope this helps kick-off your search
Tony Restell
Top-Consultant.com