This is an update of a deal I posted a few months back.
A RAM upgrade is a great way to make your PC run faster, especially if you run a lot of programs simultaneously. More RAM means less reliance on the comparatively sluggish hard drive.
If you own a desktop system, here's one of the best memory deals I've ever seen: TigerDirect has the Kingston KHX1333C9D3B1K2 8GB desktop RAM kit for $24.99, plus around $2 for shipping. That's after a $20 mail-in rebate (PDF).
The kit includes a pair of 4GB, 240-pin DDR3 sticks with a 1,333MHz clock speed. You can use them alone or with additional sticks, though if you're adding it to existing RAM, make sure all the specs match up exactly.
If you're replacing existing RAM, check your system manual to make sure your motherboard supports this size and speed.
The good news is that you can get up to two rebates per household, so you can buy two of these kits. Translation: 16GB of high-speed RAM goodness for a mere $50. (Do note, however, that you'll need a 64-bit operating system--like, say, Windows 7 x64--to take advantage of that much memory. The 32-bit flavors of Windows can address only 3.5GB max.)
Of course, even 8GB affords a nice performance boost on the cheap. Who's in?
Bonus deal: Also at TigerDirect, check out the I-Inc IP221DBB 22-inch LCD monitor for $99.99, plus $9.56 for shipping. Okay, technically it's 21.5 inches, but it offers a 1080p display and 100-plus overwhelmingly positive user reviews.