Armor Penetration Red - great for AD, bruisers or jungles like Lee Sin/Trundle

Magic Pen Red - for any AP carry

Flat Armor Yellow - must-have for nearly all junglers

Magic Resist Blue - great for bruisers or tanks

Ability Power Blue - for any AP carry

Ability Power Quint - 30 AP with doran ring at start of game is gooding yo

Armor Penetration Quint - 25 armor pen (quint+red) at start of game is gooding yo

Dodge Yellow - awesome runes especially with Nimbleness, but expensive as fark

Attack Speed Blue - great for jungle Warwick or jungle Yi fast clear

HP Quint - crap now, but useful for ultra-safe jungle Amumu/Rammus lv1 blue

HP/5 Quint - great solo lane sustain for bruisers like Jarvan or Irelia

MP/5 Blue and Yellow - mid sustain for mana-hungry carries (e.g. Sivir, Ezreal, Heimer)

Flat CDR Blue - situational and expensive for alternative builds or CDR-heavy characters

Movement Speed Quint - for certain champs like Singed