Necro-post but what the heck:

Battle of Tours, 732 - I think we all know the story being this one...

Battle of Hastings, 1066 - Same as above.

Battle of Hattin/Horns of hattin, 1187 - The Crusaders got rather owned, so to speak.

Battle of Lena, 1208 - Probably completely unknown to all non-Swedes, but it was a pretty decisive battle in (pre)Swedish history. A large (the number is uncertain, medieval soruces claim 12 000 but 2000 is a more likely figure) Danish force invaded [what would soon become] Sweden and were beaten. How this was done is not known though.

Battle of Lake Peipus, 1242 - Another famous battle. Crusaders getting owned again.

Battle of Halidon Hill, 1333 - Pretty complete English victory against the Scots. One of the first major victories of the longbow.

Batle of Crécy, 1346 - Simply deserves to be mentioned. Somewhat upsized though, and it seems to be the general impression that this was the first use of the longbow in medieval warfare...

Battle of Verneuil, 1424 - Often forgotten in favour for Agincourt and Crécy. "The second Agincourt".

Battle of Towton, 1461 - Bloodiest battle on English soil. Perfect setting in time and place for a battle as well.

Battle of Nördlingen, 1634 - The first major Swedish defeat in The 30 Year's War. A turnpoint for the war.

Battle of Narva, 1700 - A pretty complete Swedish victory against the Russians. One of my favourite battle when it comes to manouvering and strategies, second only to the

Battle of Holowczyn, 1708 - A "decent" Swedish victory against far superior numbers.

Battle of Poltava, 1709 - Total and utter Swedish defeat. 'Nuff said.

Battle of the Somme, 1916 - Another famous battle, I think you already know most about it.

Battle of the Bulge, 1944-1945 - How can you not be interested in this battle after seing Band of Brothers?