BASE - Bielefeld Academic Search Engine
On today's version of the page they describe themselves as having: 5,316,448 Pages of 400 Content Providers
From their "about" page:
In comparison to commercial search engines, BASE is distinguished for the following features:
* Intellectually selected resources
* Only document servers that comply with the specific requirements of scientific quality and relevance are included
* A data resources inventory provides transparency in the searches
* Searches full text plus meta data (depending on the resource)
* Discloses web resources of the "Deep Web", which are ignored by commercial search engines or get lost in the vast quantity of hits.
* The display of search results includes precise bibliographic data (if provided in the resource)
* Several options for sorting the result list
* "Refine your search result" options (authors, resources, document type, language etc.)
Try it - you might like it!