Need to know a couple of things such as what is your budget and does form factor matter much? Which features of your Copperhead do you like the most and want to retain, and which would you not mind missing?
Not knowing anything else, the Lachesis would be the most logical upgrade path for someone accustomed to the Copperhead and enjoyed their experience with it.
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~$50 from BB is the cheapest I can find, unfortunately you don't have your choice in color (its for the new red)
Diamondback 3Gs can be found for even cheaper (as they're more of a budget mouse by Razer standards) and have an even more similar form factor, although I don't know if that would exactly be an upgrade as they don't support ultrapolling right out of the box and also don't have memory for storing profiles for better driverless operation. While some might say the sensor is much better (and it might be for many), however if you were happy with your Copperhead's performance then that makes the sensor a non issue (as you're more than likely a higher sensitivity player).
I wouldn't normally recommend this, but since its on sale for so much, it might be an option...
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But again, if you liked what the Copperhead offered, there really would be no point in spending more on the Boomslang CE over the Lachesis, the Boomslang CE was made to please all the diehard fans of Razer's original Boomslang mouse, most of its value lies in nostalgia and those who absolutely love the form factor (granted, the form factor is pretty radical and generally is a love/hate type of deal, of course the same could be said of the Copperhead)
If you're open to other form factors (right hand only, for example) there are far more choices that become available. If you're open to spending a good chunk of cash ($80-100+), you have even more options. Logitech, Microsoft, and Razer all have some new products coming out very soon and all sport promising new technology (new laser sensors that finally trump all the older opticals in every way, hybrid wireless, etc...), however they're all right hand form factor and expensive ($100+)