Bristol Board (Available from numerous manufacturers).
This is a lovely surface to draw on, especially if using graphite pencils for fine detailed work.
Graphite can be easily lifted away (using mounting putty) to create highlights, or make adjustments. It is also bright white, which means that it reproduces well without the cream coloured cast that can occur with some off white watercolour papers.
One slight disadvantage when using coloured pencils is that the lack of ‘tooth’ makes it almost impossible to apply paler colours over dark ones. So, careful thought has to be given to where the lighter areas are in order that they can be left clear of too much colour.