I've been very pleased with my nOrh SE9 and the AKG K1000. You can get into this combo, with the Equinox cable upgrade (which I recommend highly!) for around $1200 new. I occasionally see used K1000's floating around, but unless they are going for $300 or less, I'd buy new. That way you get the warranty.
If you're thinking about something that will power speakers, I've also heard the Fisher 400 driving the K1000, and it sounded awfully good. You will, however, need to update the 400 (hey, it's 30+ years old...caps, tubes, and such will need replacing), which will cost you $$ (more if you have someone else like the Fisher Doc do it for you), in addition to the cost of the unit.
If you need something that will also drive "normal" headphones, I'd think about the RKV...but it will cost you significantly more $$.
If all you want is a headphone rig to drive the K1000, I'd opt for the SE9. You will be pleased.