Since people seem to be talking about runes a lot here are my rune pages. I think they cover most situations I run into.
AP Jungler: Hybrid Pen Marks, Armor Seals, AP Glyphs, Armor Quints
The idea make Jungling a breeze (hybrid pen and lots of armor) while still scaling your damage well (hybrid pen and AP). Also works for AP vs AD lane matchups where you are playing someone who auto attacks a lot like Annie or AP Ezreal.
AD Jungler: AD Marks, Armor Seals, CDR/Level Glyphs, AD Quints
This is for a AD casters like Kha'Zix or Lee Sin. You end up with 20% CDR just from runes and masteries.
AS Jungler: AD Marks, Armor Seals, MR/Level Glyphs, AS Quints
For jungling melee carries like Master Yi and Xin Zhao.
Tank Jungler: Armor Marks, Armor Seals, CDR/Level Glyphs, Armor Quints
This is just a preference thing since I like lasting in the jungle a long time and this maximizes my health potions and regeneration. Other perfectly viable options would be hybrid pen marks, heath/level seals, and MR/level glyphs.
AP vs Phys: Magic Penetration Marks, Armor Seals, AP Glyphs, AP Quints
This is one of those rune pages that I think you're just doing it wrong if you don't do it this way. It uses all tier one and manages to be mostly offensive, making this an amazing page for decimating your lane. AP/level is a viable choice too though if you are playing a champion who blooms at level 6+.
AP vs Magic: Magic Pen Marks, Health Seals, Mix of AP and MR or MR/Level Glyphs, AP Quints
It is harder to go offensively oriented against a magic damage champion as an AP champion because MR and AP occupy the same slot.
AP vs Hybrid: Magic Pen Marks, HP Seals, Mix of AP and MR/Level Glyphs, Mix of AP and Armor Quints
This is a complicated page. I mostly use it for AP oriented supports like Annie or Zyra.
AD vs Phys: AD Marks, Armor or Health Seals, Armor Glyphs, AD Quints
Armor Glyphs really suck but I prefer snowballing in lane and buying teamfight stats through items over taking late game stats (MR/level) that won't help me in lane. MR/level is fine though, it is a playstyle choice.
AD vs Magic: AD Marks, Health Seals, Mix of MR and MR/Level Glyphs, AD Quints
This is just a pretty efficient defensive page against magic dealers as an AD caster or carry.
AD vs Hybrid: AD Marks, Health Seals, Mix of MR and MR/Level Glyphs, Mix of AD and Armor Quints
This page is usually for AD top laners vs characters like Shyvana, but it is also good on supports who you plan to auto attack harass a lot on.
Ranged Attack Carry: AD Marks, Health or Armor Seals, Mix of MR and MR/Level Glyphs, Mix of AS and Armor Quints
For bot lane ADC mainly.
Tank vs Phys: Armor Marks, Health Seals, Armor Glyphs, Armor Quints
Rocking 27 armor and 72 hp, this page is for decimating AD champs in the top lane as a tank. This can also be used as a jungling page too, but your clears might be slow.
Tank vs Magic: Hybrid Pen Marks, Health Seals, MR/Level Quints, Health or Movespeed Quints
Health means you absorb more damage but movespeed has greater utility (roaming, dodging skillshots, gap closing).
Tank vs Hybrid: Armor Marks, Health Seals, MR/Level Glyphs, Armor Quints
Mainly for high utility supports like Thresh, Taric, or Janna.