Xerxes

This will be your primary source. GameTDB is huge and contains almost all GameCube and Wii IDs and covers, along with some other miscellaneous data like game languages similar to redump. They also have all of their IDs listed in a convenient downloadable .txt dump, which you can get [http://www.gametdb.com/wiitdb.txt?LANG=ORIG here] (starts download). The problem though is that GameTDB is not as reliable. There are invalid entries on GameTDB, low resolution/wrong covers making it hard to check entry validity (___X__ region European IDs having ___P__ region covers as a consistent problem), questionable developer and publisher information, etc. The actual IDs though are generally correct, and this is the only source other than a personal dump that contains full 6 character IDs like the Dolphin wiki uses. I would say the IDs from GameTDB are around 90% accurate, with the other 10% generally being flat-out missing IDs or false entries (for example wrong publisher code). Because this is pretty trustworthy but not perfectly so, I still recommend checking against one of the more reliable sources above before mindlessly posting IDs from GameTDB onto the wiki. However, in the case of a Wii game with no good cover scans for example, this becomes the most reliable source and there's no choice but to trust it until someone with the game comes to confirm/deny your addition.

Now this is a little tip to really help you get the best out of GameTDB. The way that the website is organized, every single ID has a neat little set of links at the top that allow you to go to the next or previous ID alphabetically. At first this might seem like an oddity but it's one of the best features of the site. This will sometimes start you down trails of investigation that can lead to finding out that, for example, the wiki erroneously contains two separate pages for the same game. The thing about multi region releases is, they often don't share a name, so sometimes overseas if a publisher is not clear that it's the same title, databases can get confused and list them as separate. However the IDs don't lie (or at least they haven't so far to me anyways), and when you find two IDs with the same 3 character prefix but different region and name, with two different pages on the wiki, this generally means that it's really the same game in disguise. If you put in the time to prove that they're the same title, and can get someone else to agree with you, then feel free to merge the pages.