Nehalem i7
Sandy Bridge i5, i7
Ivy Bridge i5, i7
Haswell i5, i7
Skylake i3, i5, i7
If you want a new one, go with a Skylake system with DDR4 RAM. Perhaps an i5-6500/6600k would be nice. If too much, can go with i3-6100 which would allow upgrade to i5/i7 in a couple years or more.