All my PCs and my Laptops have a 120GB
I put windows obviously, and then drivers and system tools like defrag, system cleaner, antivirus, browser and emailer and so on.
I install all my programs to D:\Program Files\ by simply changing the C to D
I put games to D:\GAMES\
There are some apps that do seem to prefer to go into C: and the only one I actually put there is WinAmp, however its perfectly fine in D:, it just dumps some junk to C: and so I let it all go there.
I also have my pagefile set to a set size on C: too, in the vain hope of limiting the level of fragmentation, but my C: right now, has 73% fragmentation and its a big block of red with very few blue bits LOL - thankfully thats fine on an SSD but in typical me fashion, I will defrag that anyway, just to make me feel better.
I have 40GB free on it and so that leaves plenty of room should I need to pop a file or folder onto the desktop for a bit.
I also setup my personal folders to point to other drives too!
My Docs , Pictures and Downlaods are pointed to F: cos that drive is used for junk
My Music & Videos point to E:\Music and E:\Videos because E: is my media drive, although I now use my server for all my data really, I dont actually need to do that anymore.