Below are some useful accountancy-based resources :

64-8: Authorising your agent
CWF1: Becoming self employed and registering for National Insurance contributions and/or tax
CA5601: Direct Debit Mandate for self-employed people
CH2: Child benefit claim form
P11D(b): Return of class 1a national insurance contributions due
P38s: Student employees
P46: Notice of new employee
P46: Car provided for the private use of an employee or director
CT41G (New Company): Corporation Tax – New Company Details
VAT1: Application for registration
VAT2: Partnership details 
VAT7: Application to cancel your VAT registration
VAT68: Request for transfer of a registration number
More HM Revenue & Customs forms