There are a few items which are so much greater than what else is available for the same slot that they're worth mentioning.
Mace and shield glasses gives stat increases, VERY good resists and hit lower defense. Unless you have a great weapon with HLD, plan on using these for your ultimate suit.
The crimson cincture is the only item for the apron slot which has stat increases, and those increases are very good.
The LT guard sash [replica] gives great benifits and fits in the sash slot. As far as I know, there's nothing else that fits there.
While 2% poison resist doesn't seem like much, the snake skin boots are the most commonly available foot gear with mods.
Outside of that, there are so many ways to configure your suit for super-poweredness that it would take too long to mention them all. Just follow rwek's advice in his last line and add in defense chance increase and hit chance increase to the important mods.
My archer suit cost me less than 1 million gold to build, and fits all my needs. Included artifacts are:
Dread pirate hat (300k gold paid)
Heart of the Lion (150k gold paid)
Fey leggings (looted from Dread Horn)
Conjurer's Trinket (from a no-longer available quest)
Everything else is runic and most of it cost less than 100k. My ring and bracelet come from quests that I've done and include hit chance increase, defense chance increase, dex increase and enhance potions. The suit is lacking in lower mana costs, and if I ever get rich on that character (all my characters are self sufficient) I'll rectify that oversight.
My samurai's suit costs more than I care to admit. It has:
Mace and Shield glasses
Jackal's Collar
Heart of the Lion (chest)
Fey Leggins
Stormgrip (gloves)
Primer on arms damage removal talisman
Runic sleeves with very high poison resist (the previous items only give about 30 poison resist total) and a jewelery set that includes damage increase, defense chance increase, stats increases and more poison resist.