In reply to Martin Bennett:
You should try the Siemens Gigaset phones. I have the SL565 and it is top quality all round. Better than many corded phones I've used and the best cordless one I've used - we have several different makes at work and they are all poorer. Even BT engineers have commented on the quality when sorting out a line problem a few years ago. Mine is a few years old now but I presume the quality remains.
To the OP, differences between phones is huge but largely you pay more for quality, what they can do, answer machine, Eco friendly one, whether colour rather than mono screens, blue tooth, SMS ability, how good at maintain the call when moving around, etc, and the list goes on and on! You need to narrow down your list to a must have list, and go from there. Some things are not actually promoted in the spec just to complicate matters. For example mine can text my mobile when a message is left on the answer machine which I find invaluable - no need to pay for call forwarding! One thing it does not do that a lot of Panasonics can is call barring. Pity, but the quality is so much better I can put up with that.