We have used many different bookkeeping packages. We are now recommending TAS. It seems to be a better bookkeeping package, maybe not as good for producing accounts. Also if you needed staff to operate it there seems to be many more people trained in TAS than any other package.
I have been using Tas Books with about 13 years and I am very pleased with it. It is very easy to use and the manuals and the telephone technical help are excellent. I use Tas Books 2.
Many accounts packages exist that will give you multiple company option - just buy a bureau version.
A good one is Tas Books - you really can't go wrong with it.
Sage 50 or for online - maybe www.twinfield.com which is decent software but the reporting isn't superb (although they're working on the reporting at the moment).
With the online one you pay each time you setup a new company (something like 5 euros per month extra per company) - so depending on how many companies you setup it may or may not make sense.