Note that the page Specifications & Support includes information relevant for all examination boards.
Edexcel AS and A Level Mathematics and Further Mathematics
Note the free support materials including the new guides to these new specifications.
Edexcel Specification & Sample Assessment Materials note the inclusion of a data set for AS and A Level.
Slides are available from the Summer Launch Event.
These schemes of work are very clear indeed. For each unit of work you will find Specification References, Prior Knowledge including GCSE Specification References and Key Words. For each sub-unit you will find Objectives, Teaching Points, Opportunities for Reasoning / Problem Solving, Common Misconceptions / Examiner Report Quotes.
Signing up to the wonderful Mathematics Emporium is highly recommended, note that it is a free website intended for the use of teachers of mathematics in secondary schools, regardless of what board you use. Register for an account and ensure you supply a correct centre e-mail address in your name for verification, your centre name and centre number.
Some of the older papers could be a useful source of questions.
See also Mathematics A Level 1986.