So pretty much forced to get IE | BT | LW | PD | Boots
You have one optional item, what do you choose?
Really wish there were more builds for ADC

ADC is supposed to build the highest DPS. Season 3 is about changing up items so they have more options, but that's not going to remove those options from increasing DPS the most.

You're not really forced to get those items, and I'd imagine the difference in overall effectiveness if you exchanged something like Phantom Dancer for Hurricane or Last Whisper for Black Cleaver would be pretty small. Itemization isn't cookie-cutter for all the ADCs either, an ADC like Vayne is going to build a little differently than an ADC like Graves, or an ADC like Ezreal. (Ezreal is likely getting Trinity Force or Iceborn Guantlet, Vayne is probably going to pick up attack speed instead of armor penetration)

Guardian Angel should be in that list though.

Well, i do get cimitar in some circumstances, but ga still strong.

Some new build are on good on certain champ.
Like ez is good with gauntlet.
Varus or twich with huricane.

But there will always be a build of pure dps

For Cait:

Start Long Sword + pots
Zerker's
Long Sword -> Vamp Scepter
Avarice Blade
BF Sword
Zeal
BF Sword + Vamp Scepter -> BT
Zeal -> PD
IE
Zerker's -> Furor
Avarice -> Statikk
GA

For Varus:

Start Long Sword + pots
Zerker's
BF Sword
Hurricane
BF + Vamp -> BT
BotRK
Zerker's -> Furor
GA
Mercurial Scimitar

At least that's what I've been doing. Hurricane + BotRK works great on Kog too. BroFist is sexy on Ezreal due to Mystic Shot. For the most part, I don't care about ArPen anymore because of how far Riot has scaled down Armor, and the rampant fear of BC.

You aren't really forced to get those items, it's just that they are the best ones for an ADC. Season gave more options but the same old IE, PD, BT, LW, Boots, and GA/Mercurial Scrimitar, are still the best.

Oh yeah, the Hurricane thing is really good on Kog'Maw and Twitch.