Creme De La Mer is rubbish - very thick and greasy and I didn't notice any visible effects. Personally I love L'Oreal Revitalift because it feels good on my skin (and only costs a tenner). It contains retinol which speeds up the process of cell renewal.
Another one I like is No7 Protect and Perfect - with regular use it definitely refines the skin and has come out well in trials:
http://www.guardian.co.uk/lifeandstyle/2007/ma y/03/shopping.science
At the end of the day, nothing will have miraculous effects, but keeping the skin moisturised (which means drinking plenty of water too) will help keep things 'plump'. Also staying out of the sun and using sun block (not to mention not smoking) is the way forward.
PS I've tried just about every cream - I used to be beauty editor of a daily newspaper. And the biggest con and hype when it comes to anti wrinkle cream are Freeze 24-7 (�80 a pot!) and StriVectin-SD. Both utter wastes of money!