To be honest, I think Nokia has lost the plot a bit with its new phones. I remember back when there was a choice of about 4 or 5 phones and you knew the one you wanted. Now there is too much choice for my liking, and its confusing to keep track of them all!.
Sony Ericsson seems to be making a better job of it. They are bringing out fewer phones, but they seem to be more polished, and have all the features you could ever want!
For my next phone, I will be looking to get a SE K700i. Assuming its not total pants when it comes out, it should do everything I want in a phone, and more.
You really have to ask yourself what you want in a new phone. For me, I want something small, fast, that makes phone calls and sends text messages. The SE K700i is total overkill for this, so really I should just stick with my Nokia 8310 which to be honest, is ideal already!!
www.mobileburn.com is a good site for keeping upto date with phones. Well written and very upto date. Check it out. I think the Z600 has plenty of column space on there!