Let's keep it brief and with as much speculation as possible. Expreview has found several new cards listed in Nvidia's 261.00 driver.
As expected, the GTX 580 is one of them and we're guessing you know by now that it's a high-end board slated to replace the largely unsuccessful GTX 480.
The GTS 455 was first mentioned a few months ago. We don't much about it and although it sounds like an improved GTS 450, which is based on the GF106 core, rumour has it that the GTS 455 is actually based on a somewhat crippled GF104. If this is the case, it might be a rather interesting mainstream card.
The GT 555M is somewhat of a mystery as we've never heard of it up till now. It appears to be based on the GF108 core, but we still can't confirm anything about this upcoming mobile part.