Although not greatly celebrated its something I like to remember because of my interests. The battle, which raged between June and December 1940 was the first real victory and (even though an invasion was unlikely to suceed anyway). The small numbers of the RAF Spitfires and Hurricanes were pitted against a huge amount of Luftwaffe aircraft. Luckily, due to the foresight of the commander who created a complex infrastructure of detection, command, and control the small numbers of RAF fighters had a massive advantage (as well as fighting over 'home' ground').
Some of the defences around Britain against invasion can still be found, as well as defences and other preparations. My home city has a big part here due to it being the base of Rolls Royce which created and developed the Merlin engine which powered both the Spitfire and Hurricane (and later in the war the P-51 Mustang).
There are a lot of 'what if' and 'Hitler never intended to invade' things around - but if you ever talk to someone who lived during that time then you really understand why it was such a crucial battle (as well as 'surprising' most of America that Britain could fight and win).
The wikipedia page is a decent description.