Microsoft has made public availability of latest build of Windows 8 today. Windows 8 consumer preview is available for download in both 32 bit and 64 bit architecture.
In case you have downloaded and forgot to make a note of the product key, you may use the following product keys at the time of Windows installation.
DNJXJ-7XBW8-2378T-X22TX-BKG7J
NF32V-Q9P3W-7DR7Y-JGWRW-JFCK8
YPFKW-33N3Y-M82BQ-HDGRC-HH2K8
Remember, these product keys and Consumer preview is valid till January 15, 2013 only.