generally, most guys now days (guys like us, that like extreme PC's) would go for a 60-120GB SSD for a boot drive. (drive 1) 60GB is big enough for the OS, 120GB is more than big enough for the OS and maybe a few games. The SSD gives you a nice snappy system, however, an ssd isnt required, just a nice thing to have.
For the second drive, its wise to go for a 500gb-1tb drive (or bigger) for storage. WD caviar black is probably the better choice here.
like tom said ^^ im going for a 120gb ssd and then a 2tb hdd in my build, but its up to you its speed vs storage - I find it all depends on your budget - some people just go all out and buy a ton of ssd's for everything - buring money in my opinion lol.