Interesting.. I keep one internal Samsung 840 (250gb) SSD thats only 150gb full and a 2tb external thats right at 1.3 tb full.
I don't keep any media on it. It includes tons of collected databases, reference files, and other programs I use like VMware( with virtual OS X and virtual Unix)
I also do side graphic design so Photoshop, and right about 250 gb of stock and reference images.
I'd say for a computer dedicated to working on solely programming and not storing loads of crap, a 250gb should do you for a long time. I'm also assuming from others posts that I'm a rare case of having so much stuff for programming.
I have an external HDD at 1TB and so far I've managed to fill about 400GB on it...
I'd rather copy things to one safe disk than keep films and music as CD's to get scratched and never be used again.
I've also installed quite a few programs to my external (in an attempt to keep my OS running quickly, rather than having programs not used often, filling up the registry and stuffs)
But you can have both an SSD and HDD in your pc, put the OS and any programs you'll be using an awful lot onto the SSD, and keep all your personal files or work projects on the HDD...
Now you have both speed and room!