Whiteboard Maths (previously known as Powerpoint maths) has an impressive selection of presentations designed for teachers to use with electronic whiteboards or data projectors.
Aimed at the secondary curriculum but many are also suitable for Entry Level. Sets are available on CDs or each presentation can be ordered individually and downloaded from the site. Priced at just a few pounds each and if you buy three you get one free! When you register with the site (free) you also get access to a selection of free presentations.