I will nominate in no order
Sewanee
W&L
Middlebury
Williams
Richmond
Hobart
UGA
UVA
Elon
Furman
Swarthmore in the springtime. Amazing.
I think Bryn Mawr is one of the prettiest campuses.
Cornell is one of my favorites
Cambridge (UK), Oxford (UK), Princeton, William & Mary, Yale, Richmond, Indiana, Colorado, West Point, Richmond, Middlebury, Bryn Mawr, Vassar, Sewanee. Those are the ones that come to mind today. I’m sure I’ve forgotten some.
While I put the ones above together, Cambridge (and to a lesser extent Oxford) really does stand out. I think the competition between the colleges, the growing conditions for grass, the time they have had to mature, and their tendency to move research facilities to separate areas contributes.
Some schools strike me as pretty during one visit, but not quite as nice the next. Stanford might fit into that category. Yale might be the other way around. I was cognizant of the surrounding area the first time I visited way back when, but the environs have improved significantly and it allowed me to appreciate the extraordinary architecture they have. At some larger universities, I can appreciate parts of them, but the overall impression I get is they are getting “overbuilt”.
Kenyon and Vassar were the prettiest of those we visited. We didn’t visit a single ugly campus because aesthetics were way too important to my daughter, at least when she crafted her list. I can’t even count the amount of times she researched a school and then said “Nope, it’s ugly. I can’t go there.” :))
Colby
College of the Holy Cross
Swarthmore
Lots of the campuses we visited were beautiful, but… Middlebury is the fairest of all!
Perfectly kept buildings and facilities with gorgeous matched gray stone buildings surrounding big lawns and breathtaking views of the mountains all around. My husband and I were stunned by how perfect the campus was.
Do a google search of the University of Washington quad during cherry blossom season. Hard to beat it. They also have the best view from a college football stadium. Tailgate by boat!
“While I put the ones above together, Cambridge (and to a lesser extent Oxford) really does stand out. I think the competition between the colleges, the growing conditions for grass, the time they have had to mature, and their tendency to move research facilities to separate areas contributes.”
Cambridge’s biggest advantage is that the river is integrated into the most beautiful colleges in a way that enhances the views considerably (The Backs, the Bridge of Sighs, etc). The Isis is not close enough to the Oxford colleges to provide the same vistas.
Mount Holyoke College
Miami-Fla, Furman, FSU and W&L.
I have to second both Furman and Sewanee. Furman should be classified as a botanical garden; Sewanee as a primeval forest park. Not an ugly building or spot on either campus. I never get the idea that UVA is so beautiful. The “lawn” is gorgeous but a lot of the rest is not.
We’re Virginia Tech fans so all other campuses fade in contrast due to some point or another. Some of them REALLY fade. We love the Hokie stone and how well campus in general is kept up with the Drillfield in the center. We still enjoy just walking around the Drillfield when we’re in the area.
Eckerd is very pretty for those of us who love the BIG Water scene. The college and the whole area around it is one we enjoy. Furman might be a close second for just prettiness of those we visited with my own lads - assuming VT is out of the running even though we visited it with them. Covenant wins for the best view from campus - it’s on top of Lookout Mountain in GA in an old early 1900s resort and the view is absolutely stunning.
Lehigh and Cornell
Our first visit to Lehigh, the trees were in bloom and it was breathtakingly beautiful.
Miami of Ohio is a very pretty campus.
Wellesley.
Swarthmore has a beautiful arboretum, but I don’t get why people think the campus itself is so wonderful. When I go there, not so infrequently, it doesn’t impress me so much.
Bryn Mawr, on the other hand, is like a little jewel. It’s very compact, but everything is just perfect in relationship to one another, and there’s none of the overblown grandiosity that limits my appreciation for some other well-known “Collegiate Gothic” campuses, including my alma mater.
If you like grandiosity, though, it’s hard to beat Cornell. A good deal of the campus may look like it was designed by Albert Speer, but Speer was far from unskilled as an architect. The sprawl of Cornell, and its dramatic terrain, really make the buildings and landscaping work in context.
Representing the midwest - Saint Olaf, U Chicago
Wellesley has an amazingly beautiful campus.
Stanford has always been beautiful, but since they are really generous with FA I will forever look at them fondly. Given that they have the best weather all year long, DH pointed out to me that the students there all look pretty darn good, too. I told him “Watch it” and he said that’s what’s getting him in trouble. 
I think the expansive campus helps the students and faculty all stay very fit.
I agree with Swathmore and Williams - I am glad I got to visit them both multiple times.
Yale’s campus itself is terrific, with its ancient architecture, but the surrounding urban environment is not as nice. Kind of like Fordham (Rose Hill) or Johns Hopkins - they are an oasis with a pretty campus itself, but you can’t forget you’re in the city.
Amherst also has a fantastic campus in a very pretty part of the state.
Beauty is forever in the beholder’s eye and heart.