I find myself running port scans often, and when I do I often run across odd ports that are filtered or wide open. I will be the first to admit that I have not memorized them all, so I felt it would be handy to have a nice reference guide available for when I, or anyone else, needed it. Port numbers are assigned by an organization called IANA and ports are allocated to various needs to avoid confusion. Below is a quick overview and reference chart. I hope you find this handy, and as always Enjoy!

Ports are classified into three (3) main categories:
o   Well Known Ports (Port numbers 0 - 1023)
§  Well known ports are used by system or processes run by root or with specific privileges. The port numbers range from 0 to 1023.
o   Registered Ports (Port numbers1024 - 49151)
§  The registered port numbers range from 1024-49151. Such ports are used by programs run by users in the system.
o   Private or Dynamic Ports (Port numbers 49152 - 65535)
§  Private ports are not assigned for any specific purpose. its range are from range 49152–65535

Link to the full and up to date list from the IANA organization direct:
Highlights of the Commonly Used Port Numbers and their Functions:
Port Number       | Protocol | Function
21           TCP        FTP (File Transfer Protocol)
22           TCP/UDP             SSH (ssh,scp copy or sftp)
23           TCP/UDP             Telnet
25           TCP/UDP             SMTP (for sending outgoing emails)
43           TCP        WHOIS function
53           TCP/UDP             DNS Server (Domain name service for DNS requests)
67           UDP DHCP Server
68          UDP DHCP Client
70           TCP        Gopher Protocol
79           TCP        Finger protocol
80           TCP HTTP
110        TCP        POP3 (for receiving email)
115        TCP SFTP (Secure File Transfer Protocol)
119        TCP        NNTP (Network News Transfer Protocol)
119        TCP NNTP (Network New Transfer Protocol)
123        TCP NTP (Network Time Protocol)
137        TCP NetBIOS-ns
138        TCP NetBIOS-dgm
139        TCP NetBIOS
143        TCP/UDP             IMAP4 Protocol (for email service)
161        TCP SNMP (Simple Network Management Protocol)
194        TCP        IRC
220        TCP IMAP3 (Internet Message Access Protocol 3)
389        TCP/UDP             LDAP (lightweight directory access)
443        TCP        Secure HTTP over SSL (https)
445        TCP SMB (NetBIOS over TCP)
465        TCP        Secure SMTP (email) using SSL
666        TCP/UDP Doom
990        TCP/UDP             Secure FTP using SSL
993        TCP        Secure IMAP protocol over SSL (for emails)
995        TCP SPOP (Secure Post Office Protocol)
1352     TCP Lotus Notes
1433      TCP/UDP             Microsoft SQL server port
1494     TCP Citrix ICA Protocol
1521     TCP Oracle SQL
1604     TCP Citrix ICA / Microsoft Terminal Server
2049     TCP NFS (Network File System)
2082      TCP        Cpanel default port
2083      TCP        Cpanel over SSL
2086      TCP        Cpanel Webhost Manager (default)
2087      TCP        Cpanel Webhost Manager (with https)
2095      TCP        Cpanel Webmail
2096      TCP        Cpanel secure webmail over SSL
2222      TCP        DirectAdmin Server Control Panel (Common for SSH as well)
3306      TCP/UDP             MySQL Database Server
3389     TCP/UDP RDP
4000     TCP ICQ
4643      TCP        Virtuosso Power Panel
5010     TCP Yahoo! Messenger
5190     TCP AOL Instant Messenger
5432      TCP        PostgreSQL Database Server
5632     TCP PCAnywhere
5800     TCP VNC
5900     TCP VNC
6000     TCP X Windowing System
6699     TCP Napster
7070     TCP RealServer / QuickTime
8080      TCP        HTTP port (alternative one for port 80)
8087      TCP        Plesk Control Panel Port (default)
8443      TCP        Plesk Server Control Panel over SSL
9999      TCP        Urchin Web Analytics
10000    TCP        Webmin Server Control Panel
19638    TCP        Ensim Server Control Panel
26000   TCP Quake
27010   TCP Half-Life
27960   TCP Quake III