Devo - they officially broke up in 1991 before officially reuniting in 1995
Iggy & the Stooges - Iggy made an album with both Asheton Brothers in 2003, "reuniting the three surviving founding members of The Stooges for the first time since 1974" - [Wikipedia]
Big Star* - Chris Bell's dead, but Alex Chilton got together original member Jody Stephens, plus Jon Auer and Ken Stringfellow to play the band's material for a few dates circa 2005.
(*the band was one of the only rock acts on legendary Memphis soul label Stax, and is considered insanely influential by many folks, most notably The Replacements - who released a song called "Alex Chilton" on "Pleased to Meet Me")
These last two really curled the toes of many in certain rock communities - Iggy had a serious drug problem through most of the 70s, allegedly burned a lot of bridges & most folks thought the Stooges would never live again. In the case of Big Star, Alex Chilton had famously been resisting performing Big Star songs for literally 20 years before the reunion.
I had a few more, but have been beaten to them by my smart, good-looking forum-mates
One I'm still waiting for, personally: Dave Davies to rejoin the Kinks fold....