lifeextender

I guess, though self serving, I should list My Add-In Launcher - see: http://www.mymovies.dk/forum.aspx?g=posts&t=6695

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mControl

Intelliremote for controlling the remote universally

http://www.intelliremote.com

DVRMSToolbox.  Love skipping the commercials.  Haven't tried lifeextender, but if I'm not mistaken, it removes the commercials.  For one, that makes me nervous, and two, I don't need the space since I don't archive shows.  Watch and delete for me.

Yougle.

It is utterly brilliant and fills the 5-15 minute "what the hell can I watch / listen to" gap perfectly.

Plus it has the LOLcats. Nuff said.

Mytv is a must for managing episodes and seasons of shows.

Vongo
webguide
weather plugin (probably doesnt matter which one)

This, of course, requires a subscription but we use MyNetflix almost daily to catch up on tv shows (Dexter, Heros) and watch old movies when things are slow.  Wouldn't know what to do without it.

Of course, I would also recommend the standards:
MyMovies, WebGuide

I highly recommend Vista4Cast and it's MCML plugin Extended4Cast.
It will show the weather on the start page. It will get current weather status every 15 mins, and weather forecast every 3-4 hours or so.
Take a look at http://www.vista4cast.co.uk/

The Program I can't live with out is Media Control. I haven't herd anyone recommending it for quit some time on here. Here's a cut and paste of the many features.

   *  Switching audio and subtitles streams while playing a video: works with AVI, OGM, MKV
   * Switching external subtitle files (.SRT, .SUB)
   * Switching between FFDShow presets (audio & video)
   * Setting and loading bookmarks inside a video
   * Real fastforward (and rewind) exactly like in the TV module (with 3 different speeds)
   * Switching and setting post-processing filters in FFDShow : contrast, noise reduction, crop, resize...
   * Configuration program provided to set all the options of Media Control
   * Full remote control support (6 buttons are mapped by default, this can be changed)
   * Default mapping (works in full screen while watching a video, except the blue button that is always caught) :
         o Fast forward / rewind buttons
         o Blue button : loads the startup page of the plugin
         o Red button : switches audio stream
         o Green button : switches subtitle stream
         o Yellow button : macros activator (used to call the macros set in the configuration program)
   * Live post-processing for Live/Recorded TV, as well as DVDs
   * Multiple FFDShow instances support
   * Removes black borders of videos automatically
   * Direct commands : set brightness/contrast/subtitles delay/subtitles & audio streams/... without entering the Media Control interface with the arrow keys
   * Windows Live Messenger integration : display incoming messages within Media Center interface, and answer to these messages inside the interface with the remote control or keyboard
   * Resuming : resume the video its last position
   * Change default audio device
   * Macros support : define macros accessibe with the macro activator + a button. With a macro you can raise keyboard shortcuts, launch external programs, and more... For example with a macro you can change of audio device, raise a shortcut (to change display profile) and then restart Media Center

http://damienbt.free.fr/index.php

GameEx and MyNetflix are my 2 most important infact MyNetflix has almost totally replaced my cable and we barely watch anything but MyNetflix anymore

DVRMSToolbox (I may test Lifeextender as a possible replacement soon.)
Vista4Cast/Extended4Cast
MyNetflix (just an awesome piece of software)
ArcSoft Blue-ray/HD-DVD plugin (best integration I've found...still leaves some to be lacking)
LEDSdriver (great, mostly overlooked mod/tool)
MCE Standby Tool (allows your system to sleep after updates by closing the MCE interface upon standby and starting it again upon resume...very handy!)