I realize the OP has stipulated freeing up space on his existing drive but I would like to add to the idea of increasing drive space. Thanks largely to our Windows using counterparts, I routinely see people giving away or even throwing away hard drives up to 100 GB in size. So it is possible to get an upgrade at zero cost.
Recently I bought a 2 TB Seagate drive for $88 US. Just a couple of years ago, that might have gotten me a 200G drive. That's an improvement literally of an order of magnitude, 10 times as much "bang for the buck". Maybe manufacturers can see the end of the mechanical drive in the near future. Meanwhile, users benefit.
I think it is important to remember that besides the freedom of "breathing room" newer, larger hard drives are faster, sometimes by a lot, depending on what you have now and your controllers' capabilities. Considering that hard drives are still (next to the nut behind the keyboard) the slowest moving parts of any computer system, a doubling of hard drive speed makes a huge impact for most people. This is not just in nebulous, conditional numbers. This is speed you can feel!
Even SATA II drives can achieve up to 375MB/sec or literally a full CD's worth in 2 seconds. IMHO, even if you pay yourself a value of only minimum wage for an hours work on your own stuff, a newer, larger, faster drive makes economic sense, and frosting on the cake is that your data is almost always safer.... and you're less likely to yank out hair in the process.