Space is tight for me, so I bought the "Bowflex SelectTech 552 Adjustable Dumbbells" on Amazon. They were like $300 for a pair, which was more than I wanted to spend, but they are super convenient and versatile.
Just another upvote for these. They're great if you don't have room for a dumbbell rack, and (of course) they're lighter than the standard dumbbell set.