Personally I prefer this:
Early game based on laner matchup:
When playing off meta like top Talon vs Xin or roaming against a Soraka, don't be afraid to spend 800 gold on executioner's call first item / the moment you start roaming. You'll win every time from then on assuming even or higher numbers.
AP: Hexdrinker > Serrated Dirk > Swifties/Mercury (Or don't upgrade for a later ninja tabi against AA comps) > Ghostblade > Duskblade
AD: Ghostblade > default if not ahead, Swifties/Ninja Tabi/Mobi if ahead > Duskblade
Later on:
Complete Maw if hexdrinker was bought earlier
Get edge of night if an AP champ is fed + get mercury treads
Get ninja tabi if an ADC and/or AA reliant champ like Sona/Teemo is fed in a high AD team
If you're ahead, get Tiamat.
Finally, fill in the last slots on this order:
Death's Dance = Ravenous Hydra > Trinity Force/Sterak's Gage = Black Cleaver/Last Whisper