I take no credit for these guides.  I only compiled them into one useful post.

Full credit goes to the authors, who took more time than me to post them, for creating them

Full credit to TheScottishAlien for the banner

Please make all tips in the form of gold bars. 

Currency fluctuates too much to be worth accepting.

Diamonds are also accepted.

If you know of or have a guide that you want added to the list, just post or PM the link and I will add it if it is worthy/different enough/better than a guide I have posted.

A "General" spec is not the same as a general, one size fits all spec. Notice the capitalization of the word. General means they controls minions.

Demigods are in alphabetical order to avoid any favoritism:

I've decided to start putting the day of the last update in the descriptions. If the authors could send me messages when they do a major update to their guides, I'd much appreciate it. This would benefit the community so they could know if a guide is out of date.

Resources:

Demigod Database (Interactive site that allows you simulate the building of any character.  All favor and buyable items are included as well as talent trees.  Even has a calculator to see what your projected stats would be.)

Demigod Wiki (A reference to everything Demigod.)

Generic:

A guide on Synergy (Synergy is basically the ability of your team to work well together. If your team is full of powerful demigods that don't work well together, it could lose to a team of underlevelled, underquipped demigods that do)

Gamereplays Guide List (Updated June 19, 2009  Lots of different guides for the strategist in you. Contains many strategies from how to capture flags to the calculation of armor values. Also contains links to some builds that are listed here as well.)

Enemy Demigods (Tips/Counters)  (What you need to know to be effective against all kinds of different match-ups.)

Harassing (Tips on how to effectively harass other Demigods Demigods.)

Kestrel's Tips (Random tips on gameplay, and mistakes people make that can be easily avoided.)

Learning Your Interrupts (One of the most important skills in the game, here is some information on it.)

Push Builds and Team Push Strategies (How to keep pressure on your enemy and push into their base over the period of a game.  Builds for that strategy are soon to come.)

The Cute Guide to Demigod (Image Heavy) (June 30, 2009  A guide to the basics done cute style.  Worth reading if only for the cuteness.)

The Strangler's Guide to Teamplay (Yes, this insensitive bastard wrote a guide about teamwork.)

Transitive's new player survival guide, part 1 (Great for beginners. Veterans won't find much new here, but any good strategy tips are worth a read. Never know what you will find.)

Theory Crafting: (no descriptions here, titles should be self explanatory.)

Ability Numbers that arn't listed

Starting Items Case Study

t3h best Itamz

The best damage mitigation for your gold

The best DPS for your gold

The definite guide on XP and gold

Lord Erebus

Guide to Lord Erebus (Great guide.  Contains both Assassin and General specs)

The Strangler's Guide (The idea behind this Erebus build is to combine his abilities as an assassin and his strengths as a general into a build that can maximize damage output and take out enemy demigods with fairly little trouble)

Oak

A Guide to Oak (No specific build you have to follow.  This guide tells you a priority to different abilities, and at level 10 branches off into 2 separate play styles, but doesn't have you follow a specific path.  Good guide for any Oak getting started.)

Eskendale's Guide to Healing Oak (June 25, 2009  You will not kill eveyone, but all things being equal it will be a cold day in hell before you die many a death.)

From little acorn to mighty Oak (Appeared different enough to "Not So General Oak". If in fact it is too similiar let me know, and I will remove it)

General Oak, The Damage Hose (Focuses primarily on minion damage, and skills and gear which will boost that damage)

Kestrel's Oak Build (June 24, 2009  High Survivability with some pretty good damage.)

Oak Assassin (Assassin - No Raise Dead Ward)

Not So General Oak (Assassin - Raise Dead Ward)

Queen of Thorns

A Lesson on Form (How to play the Queen of Thorns properly)

Goddess of Thorns (A Bramble Shield/Ground Spikes build, but instead of getting shambles, save points to max your skills early on.)

Handbook to Queen of Thorns (Section 5 contains a build called Bramble Burst. A build that focuses on "defense and support in various ways")

The Assassin (Almost exact same build as Goddess of Thorns but with a different strategy.  I thought it was interesting to see clone builds with different strategies and wanted to put this out there.)

The Unassailable Flower(safe) (June 29, 2009  For those new to QoT.  Keep your flower closed the entire match, stop dying damnit. You should know how to play the game competently, so general tactics are not discussed.)

Regulus

Angel (Ranged, no mines)

Auto-Attack (Self-descriptive.  3 different builds included in this guide for 3 different playstyles.)

Mine-Grenade (Mine heavy, also focuses on Mark of the Betrayer and Angelic Fury)

On Steroids (Focuses on Auto-Attack as it's primay source of damage.)

Stormcrow's (Ranged, mines included, diverse play style)

Rook

Demolition Man (No hammer slam, no boulder roll.  Just faster ways to bring down towers.)

Powerful Rook Hybrid Build (Towers in the beginning and then grabbing Hammer Slam later for a better end game.)

Pure Aggro Rook's Build (June 29, 2009  How to play Rook without towers, and how to do it well.)

The Ninja (Low cooldown, fast movement speed)

The Tank (High HP, Tower Spam, Hammer Slam)

The Towering (Combination of Demolition Man and Tower Whoring.  I couldn't justify removing the other builds for this one and as well couldn't justify not posting this one as well.)

Tower Whoring (No hammer slam. Build for building towers for yourself and tearing down enemy ones)

Sedna

Duelist (1v1 high survival. Good balance between healing and Pounce)

Ninja (Heavy support role that avoids conflicts with other DGs and focuses on movement speed for flag capping/running away and healing)

Queen of Healing (Very heal centric build. No offensive abilities til level 9.)

Tips, Tricks and Builds (a Collective Effort) (The builds are listed here (so far), but this is a great source for any Sedna questions you may have)

Why yetis are awful (Low cooldown, Pounce/Heal spam demigod killer)

  Torch Bearer

Burst Bearer (Focuses on doing lots of damage in a small window of time)

Fire and Ice (This build focuses on maximum burst damage and AoE farming by mixing fire and frost)

Slow Bearer (Focuses on creep control, debuffs, and a pretty nice amount of auto attack damage.)

The Immolation (Fire guide.  Lots of pictures (so pretty).  Strategies for every demigod as well as general strategies to play TB well.)

The Coolness (June 29, 2009  Ice, ice, baby)

Unclean Beast

A Tale of Two Beasts (Two sections, on the two most prominent and effective playstyles for Unclean Beast.)

Nightmare (attack and run speed heavy)

Ooze (A minimal mana using build that focuses on, obviously enough, ooze.)

The Anti-UB Guide to Rule them All (How to counter spit easily, and also how to counter people who know how to counter it.)

The Venom Hose (Hit and run)