The Millennium, Begin (1968)
The Millennium were largely a project assembled by pop producer extraordinaire Curt Boettcher, who had various Beach Boys affiliations and myriad production credits, as well as being part of the more deliberately psychedelic Sagittarius (whose 1968 Present Tense album is pretty damn great). Their sole proper album (followed by various posthumous releases and offshoots), 1968's Begin, is the pinnacle of the sunshine pop genre, cheesy as one might expect but still genuinely pretty and charming.
The album is at its best when more firmly embracing psychedelia, such as on the opening "Prelude/To Claudia On Thursday" couplet and the chiming "It's You," a legitimately great song (not to mention the modestly trippy "Karmic Dream Sequence #1," which finds the band approaching Jefferson Airplane territory). There are plenty of disarmingly sweet pop tunes with ringing guitars and sweeping harmonies, most notably "It Won't Always Be The Same" and the Monkees-like "Sing To Me." Given Boettcher's studio chops, it's no surprise that the album sounds absolutely wonderful; even those who can't get behind the saccharine sentiments of the genre can't deny the album sounds heavenly rolling out of the speakers.
Though largely ignored (or met with disdain) at the time, the album and related works have gotten a bit more credit in recent decades for inspiring various indie bands with a retro-pop vibe (like those in the Elephant 6 collective).
Here's some video someone worked up for "It's You":