2 channel Amp recommendation

I am looking to upgrade to a good used 2 channel amp in the 500-600 dollar range. I want a musical amp for my energy C-4 speakers. Any suggestions
Thanks in advance
Not knowing your room size and musical taste it is a little hard to make a recommendation, but since you use my favorite word "musical" you may want to look into (and see if they meet your power requirements) a used Audio Refinement integrated amp or perhaps the Joldida 302B (also used and hopefully supplied with upgraded output tubes). I have a Musical Fidelity X-A1 that I can also recommend, but it is now discontinued and would have to be found used as well. The X-A1 is not quite as soft as the other two amps but does offer more detail while maintaining musicality. None of these amps have bass "slam" with average efficiency speakers, but they do everthing else right for the price.
If you can possibly stretch your budget (or save a while longer), you might want to check out the Odyssey Stratos. This is one of the best sounding amps I've ever had in my system(s), and at about $1K is one of the best bargains in high-end audio. I feel you would have to spend $3-5K to match or better it. The build quality is amazing. Also, it has a 20yr warranty. Check it out at http://www.odysseyaudio.com or give Klaus a call (317)299-5578.
"Corkboy" has a Threshold S-200 (100 w/channel) on this site's auction for the next two weeks. It might not go over $600. I think this would be an excellent choice. Don't know where you live but his zipcode is somewhere on the left coast.
Ton: Are you looking for an integrated or a power amp?
Have a look at the Odyssey Stratos. TAS liked the amp and quite a few members here own and love the amp. Odyssey is currently running a special for $600 plus shipping per amp. If you order 2 they will convert them to monoblocks for free. Wow! 300 watt monos for $1200! I think I will buy myself a pair too! Good luck with your decision.
There's a pair of Meitner 100-watt Class A monoblocks for sale right now for $599 - that's killer. I would personally go for a 45-watt or so used tube amp, maybe the little VTL or a JoLida (the JoLida hybrids are very musical also, if you want a bit more bang for your buck). There are a couple of little Music Reference amps for sale - less power but very good sound. If you lean towards a Golden Tube amp, ask the seller if it's noisy - some of them are.