I use PRO Endure NPU, they do me just fine and only £20, although I think the BBB Hardwear NPU overshoes are probably the better value for the same price (I ride Look Delta pedals).
Before shelling out loads of cash it's worth thinking about how you use your overshoes. If you're out riding long distances for pleasure, then spend away but if you're commuting or similar where your tied up in traffic I work on the basis that with uncleating, putting on and taking off twice a day, plus weekend rides etc. they'll only last a winter anyway. The battering they get also means that even if they are in one piece come next December, the warmth and waterproof properties will probably have diminished substantially.