Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
*Boots: Mercury Treads supplements well for CC heavy / caster based team, Ninja Tabi for physical DPS happy team, and if the team lacks all of this for some reason, Berserker Greaves
*Sell Doran's blade to get second Bloodthirster
Dying a lot?
Get a Frozen Mallet early, or just build the Phage before Last Whisper. Doesn't matter.
Is the enemy team Tank only?
Get a Madred's Bloodrazor after Infinity Edge.
Are casters giving you a headache and you need some MR?
Banshee's Veil works for most cases, but if it's extreme, a Force of Nature may be viable if it's all nuking. If you're facing a Ryze/Annie.. might be a good idea for a FoN. If you're facing Morgana, Banshee's Veil will probably save you from the ultimate.
Is the physical DPS hero (Olaf, Master Yi, Sion, Warwick) destroying you?
BUILD CREDIT TO LEIRKOV
Full guide: http://www.leagueoflegends.com/board/showthread.php?t=229981