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.
Alternatively, try this site by F5UKW to find QRA locators from Google maps.
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!
Finding line of sight paths
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 by e.g. Brian G4EWJ 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.
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.