This post is a summary of the updates that have been made available in the first 3 months of this year for Media Center 2005. A requirement for all of these updates is that Media Center 2005 Rollup 1 has already been installed.
Windows XP Media Center Edition Update for Standby Mode (895678)
The Windows XP Media Center Edition 2005 Update for Standby Mode helps prevent the black screen that you may encounter when resuming use of the Media Center PC from Standby mode. LINK
Windows XP Media Center Edition 2005 Update for Intel 915g Integrated Video Adapter (895198)
This update is only for Media Center 2005 system which use an Intel 915g Integrated Video card. If your system features this video card and you are currently seeing visual artefacts on video playback whilst in windowed mode you should download and apply this hotfix. LINK
The easiest way to check if you have such a video card in your system is to right click on your desktop and select properites. When the display properties window opens select the settings tab and look at the section where it says 'display:' The wording of this area is 'Monitor/Display Device' on 'Video Card'

Update for Conflict Management in Windows XP Media Center Edition 2005 (890760)
The Update for Conflict Management in Windows XP Media Center Edition 2005 enables improved conflict management for users who schedule TV recordings through MSN Remote Record. LINK
Windows XP Media Center Edition 2005 Zoom Update (890629)
The third mode of zoom does not always work as expected when watching live or recorded TV. LINK
This update also requires the installation of the following hotfix - http://support.microsoft.com/default.aspx?scid=kb;en-us;891220
Tweak MCE
While technically being neither a patch, nor requiring rollup 1 the Media Center 2005 PowerToy ‘Tweak MCE’ is now available as a standalone download from
http://www.microsoft.com/downloads/details.aspx?FamilyID=9c02f0a8-8525-4110-aaa8-36aa8aebf2af&DisplayLang=en
Tweak MCE is a utility which allows you access to some of the more hidden settings of Media Center, which previously required manual changes using the registry editor.