Personally I swear by Vacuvin - does enough to keep wine good for a couple of days, which is all I need. After two days the wine will be drunk anyway.

Having said that there's an article that appeared this week on the Wine Spectator's website that says that the vacuum based systems for preserving wine are useless and that we'd be much better just keeping our opened bottles of wine in the fridge. It's an interesting read, also of a lot of comments: http://www.winespectator.com/webfeature/show/id/44284