If you're left with a half-full bottle of wine and want to save it for later in the week, but find the taste and body might be inferior to when it was first opened, then I suggest looking into a wine preserver.
There are different methods to preserving a bottle of opened wine, in fact, one method involves spraying a layer of argon gas (which is heavier-than-air) that would sit on top of the wine preventing oxidation from the trapped air inside the bottle - but this isn't for me. The most cost-effective method I feel is by way of vacuum.
There are simple manual pumps that float on average of $15 and automatic pumps near $40 that feature an LED display.
I decided to go with a manual pump that best fits by price scale and practicality. So I settled on a stainless steel manual pump by Oneida for $15 at a local Target store. The kit included two plugs and if I wanted to, I could purchase additional plugs (sets of 2) for $5.

Using this pump is quite easy. Just attach the rubber plug onto the bottle opening, place the pump on top and give it about a dozen pumps, and then you're done! When it comes time to enjoy the second half of the wine, simply release the pressure by moving a lever in the plug (you'll hear the air rushing in) and remove the plug with ease.
The packaging claims that the plugs are dishwasher safe, but i would just rinse under running water. The hand pump is nicely manufactured and it carries a nice balanced weight. So it's not some cheap plastic-made product that seems like it's going to break after a few months.
So if you're searching for a good wine preserver without any of the extra thrills, then I recommend the Oneida Wine Saver Pump kit because of it's cost, preservation effectiveness, ease of use, durability, and brand name.