9800GT DDR3 512MB PCI express video card died, looking for 1G replacement?
but i dont know what to order, all the 1G 9800 cards i found are no longer available, what would be the best replacement for about 100$ US? my comp is mainly used to play 2nd Life.

You had a very highend Older generation card.
Anyway I suggest you go for something more modern. But for $100 you will only get a midrange card.
9800 4 generations old. So they stopped producing them. I reccomend going for something with Direct X 11 Support. Anyway I give 2 of my suggestions below.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150542
http://www.newegg.com/Product/Product.aspx?Item=N82E16814500203
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150545
EVGA GeForce 9500GT or Radeon HD5570 will be good.
GPU buyers guide
http://www.youtube.com/watch?v=HDEVxeY_nek