Probably the next logical step up would be
Steelhawk Crossbow which drops off Attumen, the first boss in Kara.
Wolfslayer's Sniper Rifle from Big Bad Wolf in Kara is also nice.
Eventually, you'll probably want
Sunfury Bow of the Phoenix from Prince, one of the last bosses in Kara.
There are multiple options out there, but I'd suggest the Steelhawk Crossbow for now. If you're not ready for Kara, then Valanos' will work well for the time being. There are a few heroic drops that would be upgrades, but in general, Kara is probably the next logical step if you're not in there already.
Edited, Jan 4th 2008 10:00am by azwing