i'm sure you'll all argue this til the end of time, and please do so, lively debate is good. these are my picks for "best of breed" items for each category. just the most efficient, most effective, best bang for your buck items. the lists aren't ranked in order, my numbering is arbitrary
1) Teleports and Flag Locks - use them to win games. that is all
2) combat mana potions - not every DG can use these effectively, but the ones that can (Sedna, QoT, Erebus) can get HUGE mileage out of these. i've played with some pretty pro Sednas who gulp down these things like Kool Aid between levels 1 and like 8 or 9 (by then they've got real mana regen items and don't need them anymore).
1) Banded Armor - probably the best starting item for most DGs. remains useful well into the midgame.
2) Nimoth Chest Guard - the single most efficient armor piece in here, nothing beats the cost effectiveness of this.
1) Scaled Helm - its a good starter. you'll probably hock this and replace it with Vlemish later on, but this one is useful out of the gates.
2) Vlemish Faceguard - the all-star helm, the most efficient and effective one, some DGs can get enough mana with JUST this.
3) Plenor Battlecrown - the best SECOND helm you can get. its kinda terrible unless you've already got a Vlemish, but if you do its great. The Plenor + Vlemish tag team will provide the nearly bottomless mana supply that Sedna and QoT need to stay competitive.
1) Boots of Speed - a guilty pleasure really. a major convenience but they suck up an item slot that you'll probably want later. still these are popular and effective. if you can learn to make do without them though its much better.
2) Unbreakable Boots - this is truly great and the most likely upgrade to Banded Armor in the midgame. put together a package of Nimoth Chestguard and Unbreakable Boots to fill most of your basic health+mana needs.
3) Journeyman Treads- its a late game item but one of the good ones. this is nearly an artifact though.
1) Wyrmskin Handguards - this can dominate the early and midgame on the right demigod. kinda luck based due to its random nature but the proc is exceptionally powerful during levels 1-9ish both making it harder for enemies to fight back (attack speed reduction) and harder for them to run (move speed reduction). note, also works against towers and will reduce their firing rate by 15%, very useful for tower pushing.
2) Slayer's Wraps - crits are good. this multiplies with Ashkandor as well for a truly impressive end-game combo. good buy for a heavy auto-attacker in the midgame.
3) Gloves of Fell Darkur - good damage boost but FANTASTIC minion damage bonus. maybe the best non-artifact damage item for generals that use minions.
1) Wand of Speed - probably better than boots of speed. it gives you a bigger boost for a short time, but usually you only need to be fast for a crucial few seconds. equally valuable is that it sits in an activated item slot so won't conflict with your passive stat boosting items.
2) Narmoth's Ring - one of the best survivability items in the game. great health and regen and the cheapest available source of life leech.
3) Heart of Life - yeah, its fuckin great. don't think anyone will disagree about this pick. some people even think this should be nerfed. its basically like a portable health crystal/potion factory on 30 second cooldown. ridiculous.
1) Mageslayer - low cost makes it accessible pretty early. very strong offensive boost that can put alot of DGs over the top.
2) Cloak of Flames - another low cost artifact with really good stats. this makes a great upgrade to your Vlemish Faceguard for the mid or late game. great mana stuff with an offensive boost and an extremely useful activation for clearing out those big clusters of creeps that build up at high war scores.
3) Bracelet of Rage - if you can set it up properly this thing will give you and your squad just absolutely world destroying damage for 10 seconds. this is one of the strongest offensive items, though it requires slightly more cunning to use effectively than a purely passive damage booster.
4) Bulwark of Ages - starting to get pricey but this thing is unmatched defense. one of the only items that will allow you to actually survive endgame damage outputs of other DGs with artifacts.
5) Ashkandor - massive crits, massive damage, life drain, even minion damage boost. best passive damage boosting item in the game.
1) Swift Anklet - for all you speed junkies out there. great for harrassment type builds. very popular for Beast, Sedna, and Regulus.
2) Blood of the Fallen - a really strong health boost that remains relevant throughout the entire game. great for tank type builds.
3) Blade of the Serpent (Assassin Only) - strong stat boosts on top of an awesomely strong activated effect. this can replace the need to buy mana items almost completely for Torchbearer or Regulus.
4) Staff of Renewal (Assassin Only) - -20% cooldown is a very strong effect, better even than a celerity flag. it also stacks with celerity flags so you can use this to get 4 second cooldowns for your Fireballs or 7 second cooldowns for your Power of the Tower.
5) Heaven's Wrath (Assassin Only) - massively enhances early game creep farming which can lead to a big levelling advantage. can also be used to snipe at runners.
6) Ring of Divine Might (General Only) - a very large damage bonus for minion based builds. this can also be used similarly to a Heaven's Wrath to have your minions just blast apart a creep wave and speed up your farming.
7) Cloak of Night (General Only) - its like a better Warpstone combined with a worse Scaled Helm. great item. very versatile and tricky.