For Linux these are some of the distros that i have tried (i recommend them)
Ubuntu 7.10-easy to install , good for begginers (not for those from windows though cuz it doesn't have a windows like GUI at least for me !)
Kubuntu 7.10-same as Ubuntu just with KDE it's better for my opinion KDE for me has a more Windows Like Look!
OpenSuSe 10.3-Good too I got the KDE edition and it ran smooth
Sabayon - For those that like to throw win Vista effects to microsoft if you know what i mean perfect EYECANDY !
Puppy or DSL - for portable things i sometimes keep one edition on my USB just for any case it uses XFCE
and about Unix like things I used the followings:
Solaris 10 - Real BIG 4.x gigs and it doesn't have a good eyecandy however it isn't really complicated and it has some good things

it's made from SUN (Freeware)
Mac OS 7.3 - use Basilisk 2 to run it however you need the roms so legaly own a machine first and there are a lot guides to get started

Oh and it has some UNIX parts
FreeBSD - didn't use it i just got it recommended from a friend (too much cmds or what i don't know )
hope you like some of these