MathNet/MPRESS
Mathematics preprint search engine. Includes some European servers not covered elsewhere.

MathSearch
Searches a collection of mathematical and statistical preprint servers and databases.

Bibliographies on Mathematics
Search enabled database of citations for a large selection of mathematical specialties. Authors may add bibliographic lists or contextual references to their work.

Project Euclid
Full text access to the journal Annals of Mathematics; a limited number of other journals available through paid subscriptions to Project Euclid.

EULER
EUropean Libraries and Electronic Resources in mathematical sciences. Searches books, preprints, proceedings, serials, technical reports, theses, and web-pages.

Search sci.math.research
Search interface to access this newsgroup's archive.

Hypertext Bibliography Project
Search enabled database of citations for a large selection of computer science specialties. Authors may add bibliographic lists or contextual references to their work.

E-print Network
U.S. Department of Energy's search interface. Many options for fine tuning a search.

Citebase Search
Experimental demonstration of the Open Citation Project. Search citations by paper or author.

My OAI
A full-featured search engine for most of the major E-print/preprint servers. Easy to use advanced search features. Use it as a guest, or create a free account where search preferences can be saved.

SAIL-eprints
E-Print search engine. Includes some archives not indexed by other engines (see the "Data Providers" pull-down menu). Use as a guest or register and receive free targeted alerts and other personalized features.

Directory of Open Access Journals
Covers many free full-text mathematics and scientific journals (most are peer reviewed).

AMS Directory of Mathematics e-Print Servers
American Mathematical Society's directory of preprint and e-print servers.

CiteSeer.ist
E-print database of mathematics and science papers with citation information. Papers may be added by specifying the URL where their files reside.

Front for the LANL ArXiv
Easiest search access to papers posted on the preeminent Los Alamos National Lab (LANL) Physics and Mathematics preprint server (arXiv).