Specs-wise, look for the S60 platform running alongside of WiFi, HSDPA, A-GPS, and a 3.2MP camera along with 110 MB of internal memory and an microSD memory card slot on both models. The E66 slider has a slightly larger QVGA display as compared to the E71 (2.4" vs 2.36"), while the E66 is a little thicker at 13.6mm, front-to-back. Both phones will feature extensive business-oriented features including support for Microsoft Exchange, MS Office documents, and VPN access.
Don't hold your breath waiting for either of these bad boys to show up on AT&T or T-Mobile anytime soon, but come next month you should be able to find them over in Europe for somewhere around EUR 350 (roughly $500 US or so). Meantime you can check out the press release over on Nokia's website.