I'm planning on writing a fanfic featuring several characters from the Thieve's Guild, and for research purposes, does anybody know if there's an archive for all of the dialogue in the game? Much appreciated.

(For the record, I'm on the console, so CS is a no go).

Maybe imperial-library.info
Never visited it myself, but others have mentioned it, so took a quick look and it might have what you are looking for.

The imperial library as mentioned is a good start for lore, but I can't think of any comprehensive site for game dialogue. The UESP also would be a great source for information on the quests of the guild (and many dialogue entries).

For what it's worth I exported the database into a txt file. You can get it http://www.mediafire.com/?68g98hf7fwfbnxg. To find relevant entries just do a text search on key words (aengoth, devil tanto, jobs, etc.)