As usual, I'll be following chronological time rather than the "soap-opera" time that the show has used since S6. As usual, everything is taken from my timeline.
1994 - (Sometime in the summer) Dean and Sam stayed with a babysitter named Donna in Housatonic, Massachusetts. Dean develops a crush on Donna, while Sam assigns himself a summer reading list. At one point, John is gone for a full two weeks.
1996 - Dean and Sam are probably still thinking fondly of all the fireworks they set off on the the fourth of July.
1997 - (Sometime in the summer) The Winchesters hunt a werewolf.
1998 - (Sometime in the summer) Sam does research in Lincoln, Nebraska, while John and Dean hunt a kitsune nearby.
2005 - (Sometime in the summer) John Winchester teaches Adam Milligan to drive using the Impala.
2006 - John Winchester Dies.
2007 - Sam and Dean have put the dead demons in Elizabethville, Ohio, behind them, and it will be 3 months until we join back up with them. We can only assume that they spent their time living life to the fullest (Dean) and researching desperately in an attempt to save their brother (Sam).
2008 - (Sometime in July) Sam attempts a suicide mission to kill Lilith, but Ruby saves his life. Meanwhile, Dean is being tortured in hell, but is still refusing Alistair's offer to get off the rack.
2009 - Sam works as a bartender in Garber, Oklahoma, while Dean continues to hunt, either alone or with Castiel.
2010 - Dean is a twisted mess of grief and PTSD while living at Lisa's house in Cicero, Indiana. Sam body may have already been resurrected. Sam's soul is tormented in the cage by Lucifer (and possibly Michael too).
2011 - (Sometime in the summer) After discovering that Sam is alive, Dean begins hunting again while still trying to have a home-life at Lisa's. Sam's soul is tormented in the cage by Lucifer (and possibly Michael too).
2012 - Sam and Dean recover from a leviathan attack (and a psychotic episode) at Rufus's cabin near whitefish Montana.
2013 - Unknown - Is Dean still in purgatory? Is Sam still alone?....we won't find out until October!
Wow, Sam and Dean spend a lot of time apart in the summers.
And for those wondering - yes, the date that I favour for John Winchester's death is July 19th, 2006. Here's a tip though: If you ever participate in a trivia contest at a Creation Convention, in the first round of the competition they will ask if John died on November 2nd, and they'll only accept "yes/true" as an answer, even though the correct answer is "no/false." John either died on July 19th or August 5th, but based on information in S4, I prefer the July date.