Mapping tools
Finding the QRA of a site
http://k7fry.com/grid/ New site for finding locators to 10 character accuracy by clicking on a map.
Lat and Long conversion
UK postcode to Lat and Long: https://www.freemaptools.com/convert-uk-postcode-to-lat-lng.htm
Google map based site to find Lat and Long, OS grid reference and address including post code: http://www.gridreferencefinder.com/
OS NGR to Lat and Long
Convert the OS map 10 digit reference such as TG51401317 to Lat and Long here: http://www.movable-type.co.uk/scripts/latlong-gridref.html
Topographic Google map
So exactly where are the highest sites near me? Use this Google map based site overlaid with height / topographic data to find out: http://en-gb.topographic-map.com/
Overlay OS maps
http://wtp2.appspot.com/wheresthepath.htm
Portable sites
Directory of portable sites Wiki pages describing some sites suitable for ATV and microwave operation
A Google map listing known portable sites - please add yours!
Radio link and path software
The software of choice for BATC members is G0MJW Dr Mike Willis' Microwave Path Profile available here.
The ASTER mapping data is available after registration with NASA on this website. Tiles of mapping are available for each degree of longitude and latitude - east or west of the Greenwich Meridian. A typical search string for England and Wales of *N52E00* and N52E00* will give an available range of land tiles for the latitude. 5GB of data may be downloaded for N48 to N56 Northern France to Southern Scotland quite easily. The Sites.dat file is a strength of the program to easily enter repeaters, QTH and hill sites for Rx and Tx sites. It's relatively easy to add positions of further hill tops and friends QTHs using positions from Google Earth or e.g. Hillbagging.co.uk to the sites.dat file
A very useful site with "click to see the path" https://www.solwise.co.uk/wireless-elevationtool.html
Software used offline /P and at home is Radio Mobile by Roger VE2DBE. Roger's website links to the G3TVU Quick Start guide aimed at UK users which has UK-tailored versions of Radio Mobile. Ian G3TVU has done a thorough job so set aside an evening for building Radio Mobile UK.
For optical and Line of sight paths see http://www.heywhatsthat.com/
Line of Sight assessments may indeed also be possible in MicroDEM by Prof Guth of the Oceanography Dept, US Naval Academy. Leszek discusses its capabilities here.