Today is the Day of Remembrance dedicated to the 3 Apollo-1, STS-51-L Challenger and STS-107 Columbia.
info and comments from President Obama and NASA Administrator Astronaut General Charlie Bolden can be seen here.
Apollo-1 January 27, 1967 23:31 UTC
fire at the launch pad in a "plugs out" test with 100% O2 atmosphere in capsule
Command Pilot
Virgil I. "Gus" Grissom
Senior Pilot
Edward H. White II
Roger B. Chaffee

STS(SPace Transportation System) 51-L Challenger
-Teacher in Space January 28, 1986 16:38:00 UTC
Vehicle broke apart due to aerodynamic forces 73 seconds after launch
Commander Francis R. Scobee
Second spaceflight
Pilot Michael J. Smith
Only spaceflight
Mission Specialist 1 Ellison S. Onizuka
Second spaceflight
Mission Specialist 2 Judith A. Resnik
Second spaceflight
Mission Specialist 3 Ronald E. McNair
Second spaceflight
Payload Specialist 1 Gregory B. Jarvis
Only spaceflight
Payload Specialist 2 S. Christa McAuliffe
Only spaceflight
Teacher in Space

STS 107-Columbia
Launched 16 January 2003 15:39:00 UTC
1 February 2003, 13:59:32 UTC
Shuttle broke apart during re-entry after hot gasses penetrated left wing via damage sustained by a piece of foam strijing the RCC heat panel at a speed differential of over 500mph (Shuttle was supersonic, but the foam had slowed some by the time it hit the wing)
Commander Rick D. Husband Member of Red Team
Second spaceflight
Pilot William C. McCool Member of Blue Team
First spaceflight
Mission Specialist 1 David M. Brown Member of Blue Team
First spaceflight
Mission Specialist 2 Kalpana Chawla Member of Red Team
Second spaceflight
Flight Engineer
Payload Commander Michael P. Anderson Member of Blue Team
Second spaceflight
Mission Specialist 4 Laurel B. Clark Member of Red Team
First spaceflight
Payload Specialist 1 Ilan Ramon Member of Red Team
First spaceflight
STS-107 crew was split up into 2 teams, a Red and Blue team. this was done to accomodate the huge amount of science that STS-107 was assigned. While one team slept, the other worked. SHown in the following pic.

Condolences to the families, friends of these brave people. And to others involved in the Space Program who have fallen as well. Lest we forget, and let us honour their contributions with continued future human spaceflight.