CiteSeer Search engine for computer science and related matters. For all results number of citations are given which allows to estimate the importance of a paper in a given context. Most of the papers are cached and available for direct download as postscript or PDF. http://citeseer.ist.psu.edu/
ISI Highly Cited A search tool to identify individuals, departments and laboratories that have made fundamental contributions to the advancement of science and technology in recent decades. http://isihighlycited.com/
iSpecies A species search engine from Rod Page of Glasgow University. Search on either the common or Latin name of a species. Results are generated by querying other data sources. http://darwin.zoology.gla.ac.uk/~rpage/ispecies/
Meta Search Engine for Scientific Literature A multi-search tool that permits queries from scientific journals. http://www.ojose.com/
Online Journals Search Engine A multi-search tool that permits queries of a number of scientific journals. http://ojose.lanners.org/