Help:
Who is this for? Technical people - Programmers aka developers, and useful for network administrators (firewall config).
What is This all about Quite simply - it lists all port numbers, associated services and an increasing amount of programs.
Why is this Although this same list can be seen elsewhere (see credits) - navigation here is slightly different. It also has more entries then the assigned 'IANA' list (contains info for programs/services that have not been 'approved'). The data is also searchable and each port is also assigned a 'recommendation' value for programmers (ie. help to determine which port can/cannot be used)
CREDITS Thanks to :

http://www.iana.org - main content : http://www.iana.org/assignments/port-numbers

http://www.neohapsis.com - for the original main listing contents

http://www.Simovits.com - for the original trojan entries

All those people continuously adding information about port use.

FAQ:
Is it Up To Date / correct? Unlikely! - Check other sources if the information here is no good. For starters go HERE and search the page.
This is only here for easy reference!
Re "Programmers Perspective" Okay, this will likely be considered as a little incorrect by some. It is obvious that some ports are 'assigned' as defined by IANA and thus should not be used by programmers - yet this is not reflected here. One reason is that there is no reason why a developer cannot use a port designated as assigned by IANA. More reasons exist but this is enough flame bait for now ;) (will 'BitTorrent' ever have its own assignment???)
Why list all the trojan entries? 'As a developer' i probably shouldn't pick a port with many/prolific trojans associated with it (it could well be blocked at a firewall.)
Why list all the trojan entries? 2 For network traffic watchers... if there is suddenly a whole lot more traffic on a port then this list can help determine the (program) source of the packets (eg. virus/messenger)
Note: For simplicity reasons - 'programmers perspective' ignores TCP/UPD traffic types. (ie. it might be considered safe to send UDP traffic BUT NOT TCP traffic on a port)
User Comments:
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Search functionality will NOT search user comments until they have been moderated (last update time can be found at the bottom of a port list page).
Feedback/Comments: Use this form (click)
Further information: Background to ports (read both and you should start to understand that ports are like little doors - opening out on to the internet): What is a port scan? and Batten Down Those Ports.
Deeper information (and more links): http://www.akerman.ca/port-table.html
Port Requirements for the Microsoft Windows Server System.
For game server information try: www.practicallynetworked.com
Main port listing