In CoH lore, the big turning point of the Rikti War was the Alpha and Omega gambit, which took place on November 27th 2002. 50 heroes set out to the Rikti homeworld with little hope of return. Before they went, they wrote letters and sealed them in a time capsule.

Now, on the seventh anniversary of that day... the capsule has been opened.

http://www.cityofheroes.com/game_info/story/omega_team_time_capsule.html

Some of the letters have been posted on the official forums in various places. You can find them easily through the Community Digest:

http://boards.cityofheroes.com/tracker.php?do=showresults&type=community&outputType=&searchid=1492377&language=

My personal favourite is the letter from Ruin, Hero 1's archnemesis.

Gotta like a man who knows what he wants...

Heh. Funny you should mention that, as I just ran the new cape mission where you have to recover Hero1's letter that the ritiki steal...

And after having gotten it you get to read it in your clue window. And after I did all I could say was "Well DONE!".