I use to use "Quickbooks" because its very easy to use and understand, can be customised for invoices, etc, but its also very powerfull. Most accountants will be familiar with it or they will actually use it so you can just email your file to them if you want.
Its been around for ages so it must be doing its job properly.....
Loads of backup help, tutorial, etc including a search feature for finding a local quickbook expert to help explain things better if needed.
http://shop.quickbooks.co.uk/Regards
Mr H