Newegg slamming the competition with a 3tb monster drive for $129.99 and f/s too! This is in addition to a 2tb drive I've seen for $65 after $10 rebate.
Can 4tb hard drives be far off (more than 6 months)? I doubt it...
Samsung demo'd a 1tb in a single platter drive, so 4 or 5 platter 4tb drives are probably in the end stage design beta/debugging pool.