Fyodor has announced [1]a new major release of Nmap, what might just be the most popular security tool around. There is also a good interview with Fyodor [2] at SecurityFocus which details many of the changes.
From Insecure.Org:
"Changes since version 3.50 include a rewritten (for speed and memory efficiency) port scanning engine, ARP scanning, a brand new man page [3] and install guide [4], 'l33t ASCII art, runtime interaction [5], massive version detection [6] improvements, MAC address spoofing, increased Windows performance, 500 new OS detection fingerprints, and completion time estimates."
Links:
[1] http://www.insecure.org/stf/Nmap-4.00-Release.html
[2] http://www.securityfocus.com/columnists/384
[3] http://www.insecure.org/nmap/man/
[4] http://www.insecure.org/nmap/install/
[5] http://www.insecure.org/nmap/man/man-runtime-interaction.html
[6] http://www.insecure.org/nmap/vscan/