Hmmm....flowers i would/have purchase for the scent alone...
I just recently got a hoya with a blooming peduncle and it smells of butterscotch, so yummy! It's faint, maybe because only a few of the tiny flowers on the peduncle opened, but I could definitely recommend it: H. davidcummingii
(SRQ Hoyas has it if anyone wants to try it out)
My 'Firefighter' rose made it into my garden pretty much on scent alone. I really don't like thorns, so roses weren't terribly high on my list, but between the fragrance and the beautiful blooms...
I purchased a lilac from Arbor Day foundation--which was kind of a joke because the plants they give you are so small,
but lilacs are supposed to grow fast so I bought it. I ended up giving it to my mom, though, because I couldn't decide where it would go that I could still appreciate its short-lived fragrance. Now I have a hoya cutting that reportedly smells like lilac, so I'm hoping that's a better substitute.