Things have been tight, and I'd not upgraded anything since adding a 120 GB SDD. Still running with a 2.8 GHz Athlon 64 x4 630 "Propus", an AM3 socket CPU that you can't even get now. It's sneaking up on its fifth birthday (though I ordered mine about a year after it came out), making it ancient in computer years.
In the past week or so, though, I have upgraded my graphics card. I was using a PNY card with 1 GB of RAM and an nVidia 560Ti GPU; PCI Express 2. It's a HUGE card, 8.25 inches long. While the cute little Micro ATX case that I use claims to be able to fit a 10.5" card, I'd not even try, and I'm amazed I managed to fit this one in. It's power-hungry; it has two 12V power connectors in addition to pulling 12VDC from the PCI Express socket, and the size and additional cables impede air flow, which a Micro ATX case seriously needs. It's the most expensive computer component I've bought for many years, at $250.
Its replacement is an EVGA card with 2 GB of RAM and an nVidia 750 Ti GPU. Fortunately PCI Express 3 will work with a PCI Express 2 slot, but I'm losing throughput because of it. It is only 6.7" long and doesn't need the extra power connectors, so the air flow is much better. It cost 40% less than the 560 Ti card--$150.
The new card made for a bit of fun installing, because it has the new "Maxwell" chips, and one either has to directly install the proprietary driver that knows about Maxwell or add a repository with that driver packaged. I chose the latter (if by some strange chance you're reading this and are the person who set up the PPA, bless you!). If, like me, you decide to do a new Ubuntu install at the same time (don't ask...), do not tell it you want it to pull in proprietary drivers at install time; it won't get the right one, and towards the end of the install, the screen image will be stretched vertically and you won't be able to see what you're doing!
It's in and running, and running quite nicely. I have to put my ear within five inches of my computer to hear fan noise. Maxwell isn't the highest performance GPU out there, but it's excellent for performance per watt consumed.