If you share our situation - a small apartment and a very mobile baby (translate: crawling everywhere) - then you will definitely appreciate what I am about to tell you about.
As new parents, we were overjoyed and amazed by how fast our baby was able to crawl. It was really cute, that is, until it got to the point where we spent all our time chasing after our son and telling him "no" and "careful" and other words of caution. Initially, we were morally opposed to the idea of a playpen. After all, our baby is not an animal! Well, we got rid of that way of thinking very quickly! That said, we still weren't blown away by most playpens that are on the market. They were really too small and they seemed really wobbly.
Just when we were about to give up our search, we came across the l'il playzone at onestepahead.com. It's great! You can buy attachments to make it as large as you want; you can dismantle it and store it under a bed; you can bring it to the park and set it up as a confined, members-only playground; etc... Our son loves it, especially when we join him in the "playzone."
So, if you are looking for something to keep your tot contained and content, then you really should check out the playzone. And if you are worried about the idea of cooping your kid up in a pen, then you should know that the playzone is more like a "gated community" than an animal cage.