The following links are not affiliated with Logitech but offer support related information and/or additional Harmony features.

Downloadable Harmony Icons
Harmony Model Comparison Table (Detailed Listing of every Harmony's Specifications)

Bev's Harmony Info
Windows Media Center and Harmony Info
Harmony Sequences/Macros
Harmony "Sound & Picture" Button Details

The following links are "official" logitech web pages... some are more useful than others

OEM Device Support Check (Answers the question, "Can Harmony Control my Devices?")

Harmony Software Download

Harmony Software Web Interface (Not supported, but can be used when the downloadable software is not available 

General Harmony Support Information
FWIW, the entire Harmony support structure has been in serious trouble for months and at the time of this writing (11/8/09,) things appear to be getting even worse.  If you are unable to get support for harmony products, the harmony user support forum is your best bet to get help when the "official" lines of support end in a brick wall.

Not sure what the current situation is, but as I collected support links for this page, doing so exposed the fact that the  "support" links" on many logitech web pages (which still exist all over the Logitech site,) are no longer supported and, therefore, unreliable.  Worse, they act as if they are live, accept your messages which may never be seen by anyone at logitech.

From what I understand, while the old support pages and forms are still live, logitech has taken steps to make the only support incident creation through the Harmony software which you install on your pc and then only for accounts associated with each specific remote and only for the warranty period which begins the day you create an account for your remote.

This FAQ  outlines the steps now needed to connect to "official" Harmony tech support. Note, while this FAQ is "official" it is far from accurate and complete.

If the user cannot install the software and associate it with a specific remote, the only alternate options are to call the phone number found in the remote's documentation or post on this forum.

The frequently posted suggestion in the Harmony user forum; "Click the Support Link at the top of this page..."  is now incorrect (and unreliable) as following the steps from that suggestion still takes the user to those (now unreliable) links.

Harmony Support Policy (effective June 2009) Discussion  (90 days free, paid thereafter)

Current Harmony Remotes (USA)
Current Harmony Remotes (Eur)
Harmony Knowledge Base (Searchable)

Note "official" harmony site links are derived, complex and fragile... the harmony product page link broke the day the page was posted, so, please let me know if you experience broken links.