Three Boys Music Corp. v. Michael Bolton
212 F.3d 477 (9th Cir. 2000), cert. denied, 531 U.S. 1126 (2001)
The court notes that 129 songs called "Love is a Wonderful Thing" have been registered with the Copyright Office. You can search the registration database online to get more details. You'll see that both Michael Bolton and the Isley Brothers have registered a work under that title.
You can listen to both songs and compare the Isley version with Bolton's here.
As a side note, Jimi Hendrix began his music career as a back-up guitarist to the Isley Brothers in 1964.