If you plan on popping out a baby anytime soon (don't you hate that phrase?), or know someone who is or has recently, I recommend getting the Bumbo Seat.
Anyway, the seat can be used to safely and effectively sit them up in a comfy way. It seems to fit a baby's body nicely. It is made up of a foam like material and comes in many colors. As far as its uses, I think some people put it on the table so the baby can eat, (but I would do that with maximum supervision), or just use it while they need to do something like cook or clean and want to see baby nearby. You can find it at places like amazon, target and walmart for about $30. The tray that secures them in it is an additional $10.
Since it's light, portable, small and safe, I highly recommend it. Here are some pics of Devin in it for your enjoyment (10 weeks old).