The CIMT Mathematics Enhancement Programme now has its own web site (previously based at Plymouth University and, before that, Exeter University) has been one of my favourite and most used sites over the past 15 years.
100s of PDF worksheets – grouped by school year / NC levels, but many are ideal for adult use. The Year 7 area is particularly good for place value, decimals and fractions. The GCSE Revision Foundation Pack is also good. Most worksheets also have optional associated downloads such as OHP slides (also suitable for displaying on an interactive whiteboard), answers, revision exercises, lesson plans and mental maths tests. Also take a look at the Puzzles.
Continual Professional Development
Great section on common maths misconceptions with 8 downloadable resources and a help section with worked examples in 10 topics (aimed at primary school teachers but useful for any teacher that wants to brush up their maths).
Online interactive resources
A series of excellent interactive tutorials based on the printable worksheets (see above). For example, check out the Year 7 and Year 8 tutorial pages. Students can complete these online (also work well as paired activities if you don’t have one computer per student) and then print sheet with scores as evidence to put in folders or portfolios.
Embedded and contextualised resources
A great Topical Applications of Maths area with resources and lesson plans. Topics covered include: Fair Trade, lottery, global warming and many more.