We have two big Armarkat trees which have held up great for over 5 years. Sturdy too, we've had three kitty maniacs climbing and jumping on those things. I replaced a couple of the sisal posts (you can order any parts on their site) that were the favorite posts for my cats to scratch. They don't take up a ton of room, we had one for our guys when we were in a fairly small apartment. That one held up so well we have it in the house now and it still looks great, I vacuum it a lot and it looks really nice.
I just stumbled across those Go Pet Club ones on Amazon today, those look awesome too, and they are much cheaper if you buy through Amazon than their website.