Smith's group alone has around 35 publications from 2009 and 2008. It is impossible for me to send you all of them, let alone also all the papers by Pendry, Zheng, Engheta, Soukolis, Schurig, and everyone else.
I guess if you want the very, very basic/seminal papers I can list them here.
Added after 16 minutes:
Smith papers:
PRL 84, 4184 (2000) - first negative index metamaterial
Science, 292, 77 (2001) - experimental verification of negative index
Science, 308, 502 (2005) - Superlensing
Physical Review E, 71, 036617 (2005) - effective parameter retrieval
Science 312, 1780 (2006) - Transformation optics
Physical Review Letters 100, 024301 (2008) - Acoustic cloaking
Science, v. 314, p. 977, 2006 - cloaking demonstration
Those are the bare, bare minimum important papers just involving Smith. Go to their pages and look through the publications. Science is the biggest journal that publishes metamaterial-related stuff.
ee.duke.edu/~drsmith
David Smith at Duke
**broken link removed**
Nader Engheta at U Penn
**broken link removed**
Xiang Zhang at UC Berkeley
http://people.engr.ncsu.edu/dschuri/Site/Publications.html
David Schurig at NC State
**broken link removed**
John Pendry at Imperial College
http://www.waves.utoronto.ca/prof/gelefth/main.html
George Eleftheriades at U. of Toronto
**broken link removed**
Willie Padilla at Boston College
These are some of the biggest metamaterial groups in the US and world. There's so much metamaterial literature out there that it's hard to even provide a base of knowledge without knowing specifically what you want info on. There are tons of papers relating to retrieving effective parameters (esp by Smith and one by Chen/Kong), papers about improving basic metamaterial elements like SRRs, papers about theory of waves in metamaterials, papers about applications like superlenses, papers about transformation optics theory, papers about applications of transformation optics, even papers about acoustic metamaterials/cloaking.
Please be more specific about what you want and what you're trying to do.