Were a call centre and thinking of moving our phone system to a voip based setup. It seems most advice advises keeping this network seperate from the standard LAN, what switch specification would be best to support 50 extensions, perhaps you have a suggestion as to make and model or specific features to look out for. Would the fact this would be voice dedicated mean that something basic would suffice?
I would say that you haven't given us enough information.
Do you have a standard network vendor? If so, stick with whatever you're already using and just get a POE version of that.
Do you trust your employees? If not, look at enterasys and their policy management stuff. You can easily do things like make the switch only allow sip traffic and give each port a super high QOS but at the same time limit the ports to only 128kbps per port. Other vendors may have similar kit.
You have to decide -- do I want to go with high end equipment and get service contract with short turn-around times and good SLAs or do I want to get a less pricey piece of equipment and keep a spare on the shelf? Heck, with these relatively modest needs you could probably pick something decent up off of ebay. Here is where your existing IT standards will come into play.
If you don't have super strict requirements, get something that you can monitor via SNMP, that has ssh for management, and at least 2 gigabit uplinks. I've had good luck with everything nortel, enterasys and extreme, managing dozens to hundreds of these at various times. I've also had good luck with linksys and 3com -- but with a far smaller sample set. I'm sure others have good things and horror stories about other vendors.
Given your comments I'd be tempted to go for something like a couple of Cisco Cat 3750V2-48PS - they're 48-port 10/100 jobbies with PoE and 4xSFP uplinks ports. The 3750s are a proper workhorse and very capable for their cost. Also I know a number of people using just that model successfully with Cisco 3911 SIP phones.