My favorite bucking bars in order from left to right.(actually, all the ones I own). I just got the one on the far right. I haven't used it yet, but will this evening. All are tungsten. Once you go tungsten, you don't go back.
http://www.tungsten.com/bucking.html they are the manufacturer, but i think you can get them about the same price from anywhere (avery, cleveland, buckingbar.net, etc)
you should be careful with the bars though, they are relatively soft. I've dented mine in two places (dropped them on other steel)