As I've gotten older, the surf/hot rod songs haven't aged well. I appreciate them for what they are, but don't spin them very often.
Non Pet Sounds tracks?
The two albums prior to Pet Sounds, Today and Summer Days, are both loaded with good songs (especially the former) which hint at the direction Brian would take with Pet Sounds. "Let Him Run Wild" and "Little Girl I Once Knew" would both fit nicely on Pet Sounds, in terms of lyrics, production, and composition.
And the 4 Capitol albums after Pet Sounds are really solid: Smiley Smile, Wild Honey, Friends, and 20/20.
"Let the Wind Blow" from Wild Honey is stunning. Carl sings a very soulful version of this song on their 70s live album, too.
"Friends" is probably their most solid album after Pet Sounds, offbeat and beautiful.
I love all the Dennis songs from this period, especially "Be With Me" and "Little Bird."
As for the post Capitol (Brother) years, you'd be better off getting the twofer of Sunflower and Surf's Up, if you don't already have it (IMHO).