The EVGA GTX 580 Classified 3072MB, previously announced on TechPowerUp, is now available to buy according to this forum post by an EVGA product manager - in limited quantities, of course. According to Gaming Blend, this card can amazingly reach a doubled 1.6GHz core clock when overclocked using waterblocks - GTX 590 eat your heart out! This card also has custom designed VRMs to take all the extra power that the card will use, which means that they won't squeal when the card is overclocked hard and also when running intensive applications such as Folding@Home.
UPDATE: Turns out that 1.6GHz overclock was actually achieved using LN2, not water. To confirm it, click the EVGA promo link after the jump and see the extreme cooling section video, or just skip directly to the YouTube video here.The design comes courtesy of Vince "k|ngp|n" Lucido and Illya "TiN" Tsemenko who wanted a powerful card without the limitations of SLI, saying:

While competitors spend time adding dual GPUs to cards that already support SLI, increasing them to 3 slots, crippling them with only 1.5GB of memory, and/or quadrupling the price, we wanted to take a different approach. One that made sense for both gamers and enthusiasts…"With the EVGA GeForce GTX 580 Classified, we focused on the key elements that the GPU and Memory need when overclocking. Power, stability, noise ripple reduction and extreme OC mode without limits. The design was created with overclocking in mind

EVGA promo page

EVGA product page

It's currently in stock at NewEgg for $599.99

Basic specs:

Performance
NVIDIA GTX 580
512 CUDA Cores
855 MHz GPU
1710MHz Shader Clock

Memory
3072 MB, 384 bit GDDR5
4212 MHz (effective)
202.1 GB/s Memory Bandwidth

Interface
PCI-E 2.0 16x
DVI-I, DVI-I, EVBot
SLI Capable

Resolution & Refresh
240Hz Max Refresh Rate
2048x1536 Max Analog
2560x1600 Max Digital

Product Warranty
This product comes with a Limited Lifetime warranty with registration within 30 days of purchase.