J.C.
We were thinking about Ikea bunk beds last year, until a friend pointed out to me that we adults would have to climb up on the bed and make the top bunk. They might be just fine, but I didn't feel like they would be sturdy enough to stand up to my very active and large kids or the weight of my husband or me (he's a big, tall guy.)
We ended up buying a very nice bunk bed set on Craigslist, used, from a private seller. I can't remember the brand offhand, but it's one of the ones you can find in a furniture store for $2000 or more. We paid $350, mattresses included, and the set was in perfect, like-new condition with the instruction book.
Friends of mine bought a very nice, sturdy set online and they were happy with it, but it was not especially cheap (I think about $1500.)