You're falling into the trap of "What would be good right now." This is a mistake when evaluating strategy. Any choice at this stage will necessarily be too late as it requires a time and resource investment that can't be made instantly. Instead I would suggest the following:
Void Rays take a long time to build and represent a substantial Vespene investment. This should allow you to produce as substantially larger army against a Protoss player focusing solely on Void Rays. A small investment in defensive structures will keep off a small force of Void Rays, however any larger force of Void Rays is better handled by direct assault on the Protoss base as you can produce a more cost effective force.
Bear in mind that a Protoss player investing in a gas heavy strategy (like Void Rays) will have an excess of minerals. The result is that their defensive force will largely be made of Zealots. Take this into account. Additionally, they are also very likely to expand as expansions are made out of minerals and provide excess gas very quickly.
Finally, I recommend better scouting. Seeing an early second Assimilator is a tell-tale sign of a Void Ray rush.
A word to Protoss players: A Void Ray rush is not a sustainable strategy, neither are mass Void Rays before you have a Mothership out. However, Void Rays do complement a Tier 1/1.5 force very nicely, especially armored units with High HP.
As far as i remember marauders do additional damage against stalkers, so your best option would be a mix of zealots, sentries and stalkers.
Zealots will take damage away from the stalkers unless the enemy focusses his fire (which then would allow the zealots to close in on the marauders). The sentries reduce the damage from the marauders, giving you an important advantage. They can also block his retreat or cover yours and cut of parts of his force. The stalkers can either blink in (warning: dangerous) to quickly get in range as soon as the enemy starts attacking the zealots or - with a little micro - you can blink out as soon as a stalker looses his shields.
Another option, though more long term, would be to switch to air as marauders are ground-only and it might be possible that he focussed too much on marauders so he has little to no anti-air.
Best Answer
The main problem with carriers only really arrives if you allow your opponent to build a ton of them. Alone, like Carl Clover said, they're very weak.
The secondary problem with carriers is that they're often accompanied by a mothership, which complicates matters.
One of the best ideas to counter a protoss dead-set on going carriers is to scout and provide early pressure if you see him teching quickly to a fleet beacon. He's probably spending so much money on those buildings that he has a comparatively weak army, and you should be able to do a good deal of damage.
Often the answer to a question of "how do I counter X high tier unit?" isn't so much about countering that unit once it's built, but preventing it from coming out at all.