Guild Wars 2

With options like these:

Light – Medium – Heavy
Asura – Charr – Human – Norn – Sylvari

That is easily done in game with the wardrobe.

Khisanth.2948:

That is easily done in game with the wardrobe.

I’m not always on GW2 though

I do not know of any website with the individual items that you can toggle previews of with other pieces of armor.

That functionality is in-game though.
Go to your bank and select the Wardrobe Vault tab and then mix and match to your heart’s content in search of your desired look. Only thing is that you can only preview on the species of the currently logged in character. If you do not have a charr, but want to mix and match armor on a charr to see how they look, you will need to roll a charr and then progress to a city to view your wardrobe with that species character.

Chrazel.7085:

Khisanth.2948:

That is easily done in game with the wardrobe.

I’m not always on GW2 though

Ah.
I suppose the only way to do it out-of-game would be to visit a site like Argos-soft and then save the images of the full armor sets for the desired species/gender/armor weight and then manually copy-paste sections of armors around in Paint or something to find a desirable mix and match look.