I've decided to focus on the useful stuff. The things that I do not mention are not necessarily useless, but I personally would consider them less cost-effective and worthwhile than the items mentioned below.
1. Swift Anklet: The 15% speed boost is good by itself, but combined with Boots of Speed or the speed abilities of certain demigods (e.g., Sedna and UB), it can be shockingly effective.
2. Blood of the Fallen: Enough said.
3. Staff of the Warmage: Good early-game boost to mana, plus a small damage bonus.
4. Amulet of Teleportation: A very viable choice. Frees up a consumable slot, and the cooldown time is not too bad.
5. Cape of Plentiful Mana: Combined with 1 or 2 of the better mana helms, this should satisfy most mana needs during the game.
6. Blade of the Serpent: I never use it, but it definitely appears useful.
7. Mard's Hammer: Good damage boost.
8. Cloak of Night: Can save your arse if you are being pursued by a faster opponent. Instant cast time FTW.
1. Scalemail: When you need armor, but can't afford the high-end stuff. Great for early and mid-game.
2. Banded Mail: When you need a health boost, but can't afford the high-end stuff. Again, great for early to mid-game; also has a tiny bit of health regeneration.
3. Nimoth Chest Armor: One of the best, most cost-effective armor sets in the game.
4. Hauberk of Life: My first preference amongst the medium-priced armor.
5. Groffling Warplate: Second only to Godplate.
6. Godplate: Very expensive and late-game, but, well, god-like. Provides very strong buffs for minions.
7. Boots of Speed: Best when combined with other speed items or abilities.
8. Unbreakable Boots: One of the real gems of the game. Affordable and provides very noticeable improvements to health and mana. They are actually a better pick than most mid-priced armor.
9. Gauntlets of Brutality: Should be a part of every damage-stackers wardrobe. Great for the cost.
10. Slayer's Wraps: Expensive, but probably the only other gauntlets worth buying for the price (besides GoB).
11. Vlemish Faceguard: Best early- to mid-game mana item, period. Puts to shame the pricier Theurgist's Cap, Vinling Helmet, and Hungarling's Crown.
12. Plenor Battlecrown: Best mana item for the money. Second to the Vlemish Faceguard only due to lesser mana regeneration.
13. Nature's Reckoning: I do not use this, but the mana boost and random lightning bolt seem worth the gold.
1. Capture Lock: Enough said.
2. Teleportation Scroll: Don't leave home without it.
3. Potions: All have their usages. I prefer the rejuvenation potions since they give both mana and health.
4. Sigil of Vitality: Probably the most effective of all health-related consumables, but seems to be the most underappreciated by the average player. (OMG!!! That UB had 9000 health! Ahh, no, he had 6000 health and just activated a sigil for a 50% boost.)
5. Universal Gadget: requires a little micromanagement, but can be very effective and versatile.
Most of these items seem fine to me. My games rarely last long enough for anyone to get an artifact. but I have used the "lower-end" stuff without complaint (e.g., Heart of Life, Orb of Veiled Storms, Mage Slayer, and Cloak of Flames, etc.). My favorite is Ashkandor. I've never had the All Father's Ring, which looks like a game ender.
Conclusion: Brad, I would say take a hard look at the Favor Items, Helms, Gauntlets, and Boots. I would be surprised if more than 6 of the Favor Items are used by 90% of players. With the exception of the Vlemish and Plenor helms, the rest of the helms are overpriced and underpowered. Same for most gauntlets and boots.