Dragon Age Origins Walkthrough and Cheats

Opening Locked Chests - Unlocking chests and doors without a key is a thief-only skill, and their rank in the skill has to be high enough for the task. Injuries can cause a thief to temporarily be unable to open chests and doors they otherwise could. There's no way for non-thieves to bash them open except in specific, storyline driven instances, like kicking in certain doors in Redcliffe, or using a certain shapeshifting form within the Fade. However, typically the contents of the locked chests are similar to the contents of unlocked chests, etc, so you're not missing much if you don't open them, just the experience the thief would get and extra items to sell a merchant.

Curing Injuries - Injury kits cure those persistent injuries that lower your party's stats; the stronger the kit, the more injuries it can cure at once on the same character. Injury kits can be purchased in limited amounts at merchants, or can be crafted by an herbalist if they have the recipe and sufficient skill. A free way to cure wounds is to take your party back to camp. You don't have to sleep or do anything special, just be at camp, and the injuries will heal.

Gauntlet Bridge Puzzle Solution - Check out The Missing Manual. They have hints for those who just want a nudge in the right direction, as well as the full solution for those who just want to be done with it, on their Gauntlet Bridge Puzzle page. They plan to add more puzzle solutions, and have lots of other useful Dragon Age information too. It's worth a look.

What's the deal with landmarks? - Occasionally, you'll see a landmark marked on your map. When you find it and click on it, if you have the war dog in your party, the game will say something about your dog being interested in it. Switch to your dog and click on it again for a benefit.

The standard possible companions:

Alistair - Warrior Templar
Dog - Mabari War Dog
Leliana - Rogue Bard
Morrigan - Mage Shapeshifter
Oghren - Warrior Beserker
Sten - Warrior
Wynne - Mage Healer
Zevrahn - Rogue Assassin

It is very possible to miss opportunities to have companions join your party, or even antagonize them into leaving. You have to be careful with the conversation options when you meet them, and listen closely to their personalities and approval/disapproval as you adventure with them. Each has gifts they like, and enjoy being listened to, so if your approval ratings with them start to slip, these are ways to bring them back up again.

For more about the companions:
Dragon Age: Origins Companions Locations and Gifts CheatSheet
As spoiler free a list as possible while telling you where and how to get them, and what kinds of gifts they like.

Or:
Wikia Companions Section
With more information and entries on speculated, temporary, and downloadable content companions.

You get two specializations related to your class to further customize your character. Specializations can be taken at level 7 and 14, if you've unlocked them. They can be unlocked at any level. They're unlocked by learning from an NPC or buying a manual from the game's NPC merchants.

Companions join the party with one specialization and are able to take a second later.

The specializations are:

Warrior:
Berserker
Champion
Reaver
Templar

Rogue:
Assassin
Bard
Duelist
Ranger

Mage:
Arcane Warrior
Blood Mage
Shapeshifter
Spirit Healer

Specialization benefits and skills, and who teaches them or where to buy a manual can be found at this Dragon Age Specializations article on Wikia.

Dragon Age: Origins Walkthrough
This is the best text walkthrough I've seen for Dragon Age. Includes origins and screenshots.

Dragon Age: Origins Video Walkthrough
Check out this youtube channel's Dragon Age Origins Playlist for a video walkthrough of the game, continuing from Part 1, posted above.

Dragon Age Origins Cheats for PC

Dragon Age Origins Achievements for Xbox 360

Dragon Age Origins Trophies for PS3

Dragon Age Origins Wiki on Wikia
With articles on the companions, characters, the origins, locations, specializations, and more.

Bioware's Dragon Age Wiki
With articles on lore, characters, crafting, combat, magic, and more.

BIoware's Dragon Age Origins Forums