Below are some useful links to various navigation related products and websites that I personally think are good and would recommend. All links open in a new window.
Disclaimer: I have no association with any of the companies and these are not affiliate links so I don't make any money from click throughs.
Ordnance Survey Maps
Maps created by the national mapping agency of Great Britain. These familiar maps come in two handy scales suitable for outdoors use: the orange Explorer 1:25,000 series and the smaller scale pink Landranger 1:50,000 series. They also come in standard paper or as a weatherproof "Active Map", although personally I find these a bit chunky. And whilst digital mapping has changed things in recent years, it's still highly advisable to have a paper map stashed in the bottom of your pack.
An alternative to the more well known Ordnance Survey maps but equally great and designed specifically for use when out walking in the mountains of the UK. Be sure to check the scale you're using as they come in 1:25,000 and the less common 1:40,000 scale. Also has ranges that specifically cover mountains and national trails of the UK.
Silva Expedition 4 Compass
Silva make some of the best, most reliable compasses and the Expedition 4 is the standard by which all others are measured. You'll spot these in the hands of grizzled mountain guides, weekend warriors, and swinging from the neck of bedraggled Duke of Endiburgh Award participants.
Ultimate Navigation Manual
The title kind of says it all and really opened the eyes of many people, myself included, as to the depth you can go with navigation. Very well written with great explanations and diagrams.
Fell Running Guide
Dave Taylor is, as you might guess from the title, a fell running guide and a navigation guru. His weekly "Navigation Task" videos challenge you to test your navigation skills in various ways and are a good way to apply thoery to practice.
Ordnance Survey Digital Mapping
The digital version of the Ordnance Survey maps. The free version gets you access to the standard maps and aerial views whilst using the familiar larger scale maps does require a subscription, equivalent to the cost of 2-3 paper maps annually (free trial available). A subscription does open up other features too though such as using the companion smart phone apps giving you large scale OS mapping on your phone plus the ability to print your own maps, handy when you just want a small section and without the worries of ruining your paper maps in the inevitable British deluge. Also you have the ability to create and view routes, great for planning.
A simple app for your phone, which, whilst not a full blown digital mapping app, does a good job of letting you know your location as either latitude and longitude coordinates or an Ordnance Survey grid reference. A great tool to take out with you when practising your navigation and you want confirmation of where you are.