One of the finest guitar solos ever is Terry Kath wailing away on “Twenty-five or six to four” by Chicago
See, to me that solo sounds like Winter just spent the previous three weeks listening to “Eat a Peach” non-stop.
“Jane” by Jefferson Starship had one of my favorite solos of the late 70’s. It was a top 20 song in 1979.
Among many greats already mentioned, I’d like to add Sister Christian by Night Ranger. Unfortunately, many radio stations edit the solo for this song almost completely out, so it’s certainly possible that many of you have never even heard it.
#65, #1, and #1 on US singles, US mainstream rock and UK singles respectively, according to this site.
Money was also well into the top 40 and has a good guitar solo.