ManualsLib - Just enter the keywords in the search field and find what you are looking for!
ManualAgent - Manuals and guides
Internet Archive Manual Library - Internet Archive Manual Library is your go-to source for viewing the big collection of datasheets, instructions, and guides written for a wide range of products.
Manuzoid - Repository that includes user manuals for various products
Manula - Manula is an online software for creating user manuals.
Dozuki - Dozuki is a web-based tool for creating and distributing step-by-step documentation.