YouTube/Video Utilities
Image: Salvatore Vuono /

Downloading services (note: these may not comply with the YouTube TOS (terms of service)

Clipnabber: download YouTube videos in FLV, MP4, 3GP formats. grabs user-specified excerpts (by time) from YouTube vids and provided embed code uses a bookmarklet that is added to your browser

DownloadHelper for IE:
DownloadHelper for FF:

Zamzar: general-purpose file format conversion site, supports video downloading

AVC Free:

Editing services
TubeChop: "chop" or select a segment from a YouTube video

DVD Ripping
Handbrake: Open source, multi-platform
RipIt: Mac only

Media Players

Alternative URL
SafeShare: repackages YT video without surrunding elements

Video Converter/Ripper/Burner
Freemake: requires download, .net utility

Converter: converts pretty much any file format