I have a Vacuvin system that I use to preserve partially-drunk bottles.  I like the idea of the system, but I can't decide if it actually helps. For those of you that like gadgets, you might want to try Private Preserve (I've seen it on Amazon.com for about $7), which sprays a fine mist of nitrogen into the bottle to keep the wine from coming into contact with oxygen.  Since I'm not really into extra chemicals, I haven't tried the system yet. 

I've mentioned before that I store leftover wine in the fridge.  This seems to be the most cost effective and tasty fix.  But here's another option that is making a come back: boxed wines.  I know, I have an inherent aversion, too, especially when I remember the pink stuff that was so popular in the early 80's.  But some great wineries are getting on the eco-friendly box bandwagon (less waste, no possibility of corking - what's not to like?). And these wines use a bag system that forces the wine downward, collapsing from the top as it is poured.  That means oxygen, that wine spoiler, doesn't have a chance to sneak in.  Many boxed wines - I mean casks (as they say in Australia) - tout a month of freshness.  Added is the benefit that some of these boxed wines are very affordable: a 3 liter box equals 4 bottles, and many boxes sell for around $20.  Yellow+Blue, Black Box and Killer Juice have gotten some good hype, as have Banrock Station and  Hardy's. 

ABC's boxed wine video coverage:The Boxed Wine Boom