There are a number of really useful websites that have great information on them. I have tried to provide as much useful information here on this site as I possibly can. That said there are many other webmasters who also provide a great deal of information which I think you will find useful.
If you are looking for parts to fix up an old Elgin watch, then this is a very good website. It lists almost every Elgin by grade, and then displays all the various parts associated with that grade. You can also key in the part number and it will display all the grades, and the exact location of where that part is used. The good news about that is that it allows you to use various parts from other grades of watches that will work for your own movement.
Elgin Watch Collectors Website
This website has been around for a long time and has lots of useful information. It is an old site but it still contains a lot of helpful and useful information, which you may find interesting. Click here if you would like to view it.
This is another useful site with some great information. In particular it is good for doing look ups on serial numbers which is useful for working out the year your Elgin was made. I have a post here on those numbers with a table or you can check your number out on this website.