Ubuntu will probably be a good choice for a complete newbie coming over from Windows or Mac. Likewise,PCLinuxOS, Dreamlinux, sidux are excellent alternatives also besides those (e.g. openSUSE and Mandriva) already touted by other TDers.
If those with some IT background or prefer a more hands-on, technical OS, the BSDs (e.g. FreeBSD, OpenBSD, NetBSD and DragonFlyBSD) should be evaluated. A simpler, gentler, less intimidating introduction to BSD (FreeBSD that is) will be PC-BSD and DesktopBSD.
Perhaps a useful place to learn more about the myriad of GNU/Linux distros, BSD flavours and even Solaris derivatives (such as Nexenta and BeleniX) will be DistroWatch.com: Put the fun back into computing. Use Linux, BSD.
For the curious n00b and advance user alike, the following links should be of some value. Do check them out:
[Phoronix] Linux & Solaris Hardware Reviews
polishlinux.org » Why Linux?
PhoroLinux — Howtos, Screenshots, and Tips for Linux
Ubuntu Geek--Ubuntu Linux Tips,Howtos&Tutorials|Edgy,Feisty,Gutsy,Hardy
Ubuntu Home Page | Ubuntu
Ubuntu Forums
Ubuntu | HowtoForge - Linux Howtos and Tutorials
Ubuntu Linux Tips & Tricks
https://wiki.ubuntu.com/UbuntuWeeklyNewsletter/
Planet Ubuntu
Planet GNOME
Linux on Desktop
https://wiki.ubuntu.com/
The Daily Ubuntu - Daily Ubuntu Applications
Hope this helps.![]()