1 taken from http://auntitled.blogspot.co.at/2010/07/identified-ubuntu-version-from-ssh.html and extended:
4 Debian 4: SSH-2.0-OpenSSH_4.3p2 Debian-9
5 Debian 5: SSH-2.0-OpenSSH_5.1p1 Debian-5
6 Debian 6: SSH-2.0-OpenSSH_5.5p1 Debian-6
7 Debian 7: SSH-2.0-OpenSSH_6.0p1 Debian-4
10 Ubuntu 5.10: SSH-2.0-OpenSSH_4.1p1 Debian-7ubuntu4
11 Ubuntu 6.04: SSH-2.0-OpenSSH_4.2p1 Debian-7ubuntu3[.x]
12 Ubuntu 7.04: SSH-2.0-OpenSSH_4.3p2 Debian-8ubuntu1[.x]
13 Ubuntu 7.10: SSH-2.0-OpenSSH_4.6p1 Debian-5ubuntu0[.x]
14 Ubuntu 8.04: SSH-2.0-OpenSSH_4.7p1 Debian-8ubuntu1[.x]
15 Ubuntu 8.10: SSH-2.0-OpenSSH_5.1p1 Debian-3ubuntu1
16 Ubuntu 9.04: SSH-2.0-OpenSSH_5.1p1 Debian-5ubuntu1
17 Ubuntu 9.10: SSH-2.0-OpenSSH_5.1p1 Debian-6ubuntu2
18 Ubuntu 10.04: SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu3
19 Ubuntu 10.04.1: SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu4
20 Ubuntu 10.04.2: SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu{5,6}
21 Ubuntu 10.04.3: SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu7
22 Ubuntu 10.10: SSH-2.0-OpenSSH_5.5p1 Debian-4ubuntu{4,5}
23 Ubuntu 11.04: SSH-2.0-OpenSSH_5.8p1 Debian-1ubuntu3
24 Ubuntu 11.10: SSH-2.0-OpenSSH_5.8p1 Debian-7ubuntu1
25 Ubuntu 12.04: SSH-2.0-OpenSSH_5.9p1 Debian-5ubuntu1.1
28 FreeBSD 7.0: SSH-2.0-OpenSSH_4.5p1 FreeBSD-20061110
29 FreeBSD 7.2: SSH-2.0-OpenSSH_5.1p1 FreeBSD-20080901
30 FreeBSD 8.0: SSH-2.0-OpenSSH_5.2p1 FreeBSD-20090522
31 FreeBSD 8.1: SSH-2.0-OpenSSH_5.4p1 FreeBSD-20100308
32 FreeBSD 9.0: SSH-2.0-OpenSSH_5.8p2_hpn13v11 FreeBSD-20110503
35 openSUSE 10.0: SSH-2.0-OpenSSH_5.0
36 openSUSE 10.1: SSH-2.0-OpenSSH_5.1
37 openSUSE 10.2: SSH-2.0-OpenSSH_5.2
40 CentOS 4.x: SSH-2.0-OpenSSH_3.9
41 CentOS 5.x: SSH-2.0-OpenSSH_4.3
42 CentOS 6.x: SSH-2.0-OpenSSH_5.3
45 Fedora 12: SSH-2.0-OpenSSH_5.2
46 Fedora 13: SSH-2.0-OpenSSH_5.4
47 Fedora 14: SSH-2.0-OpenSSH_5.5
48 Fedora 15: SSH-2.0-OpenSSH_5.6
49 Fedora 16: SSH-2.0-OpenSSH_5.8
51 complete removal of version string seems to be not desireable: http://www.snailbook.com/faq/version-string.auto.html