In launch order:

Explorer 11 (1961)
OSO-3 (1967)
Vela (late 1960s–early 1970s)
SAS-2 (Nov 1972)
COS-B (Apr 1975)
HEAO-3 (Sep 1979)
Granat (Dec 1989)
Gamma (Jul 1990)
Compton Gamma-Ray Observatory (Apr 1991)
HETE-2 (Oct 2000)
INTEGRAL (Sep 2001)
Spectrum-X-Gamma (2001)
Swift Gamma-Ray Burst Explorer (2003)
AGILE (2007)
Fermi Gamma-ray Space Telescope (2008)