Get a bird feeder, or two and hang it outside your window. I call this "kitty TV". Mine will watch for hours, and they get so excited when they see the birds! You can get a cheap one at Walmart, and a huge bag of bird seed lasts a long time.

I also used to have a fish tank that the kitties really liked. I tried having just a regular fish bowl, but it drove Bentley crazy to the point where I actually had to take the fish to work! Bentley was trying to knock the bowl over, and even tried opening the bathroom door after I put the fish in their.

Good luck. After I moved into my own apt with no other animals, Bentley was upset and lonely and it broke my heart (and drove me crazy!). I ended up getting another kitty, but you have to do what's best for your own situation. You can only take on so much.