Libraryland, astute purchases combined with staff creativity made the library awesome; Lester Public Library in Two Rivers WI really got a bang for their Star buck. And, of course, if you don't know Rachel Moani's blog, you must get her on your feed. She's a librarian/designer/artiste extraordinaire and I pick up a ton of ideas from her.
Kids are our main decorators. We usually hold an event at all three libraries during the second week of the SLP and let them create on our behalf - sometimes with sidewalk chalk; sometimes with window paint; sometimes with left-over craft materials. We put out the stuff and the kids in true "D.I.Y. Make-over" go creative on us.