I've been subscribing to 360radar for 6 months now and was on it as a tester for about a year prior to that, I highly recommend joining, great for heads up if you are into the military stuff and excellent value for money (£20 per year or £6 for 3 months).
Here's a bit about it including a link on joining:
360Radar.co.uk is a new aircraft tracking system which tracks civilian and military aircraft across the UK and Ireland. The aircraft can be tracked within a web browser which works perfectly on desktop (PC and Mac) as well as mobile (Android and iPhone). We track aircraft using a combination of ADSB, MLAT, FLARM and JAERO data. Soon it will be adding support for AIS, AirWhere and PilotAware data too.
Contributors of ADS-B & MLAT data get free access to it whilst non-contributors will pay £19.99/year (or £5.99 for 3 months) which goes to paying for the six webservers needed to run the system. There are plenty of screenshots of the site in use further down the page so you can see how it performs. If you’d like to test it out you can sign up for a 48 hour free trial here
http://signup.360radar.co.uk or just ask any of the existing users for their impressions of it.