Here are several external links that I've found to be helpful in playing Mass Effect 3 Multiplayer. This is mostly for my own reference, in case my computer crashes and takes my bookmarks with it. Feel free to comment with any links you find useful.
Mass Effect 3 Multiplayer Discussion Archive
There is a lot of information out there that isn't allowed on the wiki because it isn't stated in game, so Bioware Social Network (BSN) user randomfoo created a Google site that serves as a hub to many helpful discussions from the BSN.
Gameplay Data and Mechanics
Bioware Gameplay Designer Eric Fagnan gives some specifics about combat, including hidden weapon and power multipliers, the effects of enemy armor protection, and shield gate.
Data Mined Game Mechanics
This is a long post compiled by BSN user GodlessPaladin. It goes in-depth into the mechanics, including powers, weapons, amps, melee damage, enemy weak points, and enemy wave budget.
Multiplayer Class Builder
You can see how different choices in skill trees will affect how much your multiplayer characters can dish out without wasting a "respec" card.
This is a general link for the multiplayer manifest on the Bioware Social Network (BSN). After you sign in, it will show you what you have unlocked and what you have yet to unlock, as well as your level of consumables (e.g. medi-gel, ammo upgrades).
Premium Spectre Pack Stats Spreadsheet
The store is seriously frustrating, and Bioware hasn't revealed their algorithm for how often "ultra-rare" weapons drop from packs. A few BSN users are tracking their PSP purchases in order to establish a baseline.
Multiplayer Manifest Badges
Another BSN user (GuyBlade) created completion badges, which will show manifest completion in pie charts, as well as how many packs it will take, on average, to unlock everything.