Musical Acts You Have Seen both as headliner and as opening act
 

I'm including only acts that have toured on a national/international scale, but if others want to include local or regional acts, knock yourselves out.

Pixies: opened for Love And Rockets

Roger McGuinn: opened for The Band (classic lineup)

Johnny Dowd: opened for Pere Ubu

The Dickies: opened for TSOL--Black Flag was the official headliner but I didn't stay to see the current Black Flag tribute band that Greg Ginn is touring with

Karla Bonoff: opened for Jackson Browne

Todd Rundgren: opened for Daryl Hall & John Oates

Sierra Hull: opened for Uncle Earl

John Fogerty: opened for Willie Nelson

Scrawl: opened for Great Plains, and for Wussy

Great Plains: opened for Nick Cave & The Bad Seeds, and for Half Japanese

Webb Wilder: opened for Jim Lauderdale

Riders In The Sky: opened for Mark Willis

VOLK: opened for The Electric Six

I've seen indie pop extraordinaire katie dey both headlining a show with an industrial artist and opening for a screamo concert. It's an interesting combo, to be sure.

Breeders opened for Nirvana
Magik Markers opened for Sonic Youth
Boris openend for Amenra

Low opened for Mercury Rev
Bill Callahan opened for Low
Rivulets opened for Low
Dark Dark Dark opened for Low
Claire M Singer opened for Low
Chantal Acda opened for Low (when she was in sleepingdog)
Chantal Acda opened for Nils Frahm
Love Like Birds opened for Rivulets, Dark Dark Dark and Scot Matthew
Glenn Branca opened for Thurston Moore
Disappears opened for Thurston Moore
Dans Dans opened for Thurston Moore (unfortunately I have no recollection of their set)
Flying Horseman opened for Mono