Merriam Webster: http://www.webster.com/
Ciba Online: http://www.iciba.com 

Databases and Search Engines

IEEE Xplore:   http://ieeexplore.ieee.org/
ACM Digital Library:   http://portal.acm.org/dl.cfm
SIAM:   http://www.siam.org/
Google Scholar:   http://scholar.google.com/
CiteSeer:   http://citeseer.ist.psu.edu/cs
ACM SIGMOD:   http://www.acm.org/sigmod/
SIGMOD Record:   http://www.acm.org/sigmod/record/
IEEE TCDE:   http://www.ipsi.fraunhofer.de/tcde/
Data Engineering Bulletin:   http://www.research.microsoft.com/research/db/debull/
VLDB:   http://www.vldb.org/
VLDB Journal:   http://www.vldb.org/dblp/db/journals/vldb/index.html
ACM SIGMOBILE:   http://www.sigmobile.org/
DBLP Bibliography:   http://www.acm.org/sigmod/dblp/db/index.html
MathWorld:   http://mathworld.wolfram.com/

Simulation Tools

Simulation Tool List:   http://www.idsia.ch/~andrea/simtools.html
NS-2:   http://www.isi.edu/nsnam/ns/
C-Sim:   http://www.mesquite.com/
OMNeT ++:   http://www.omnetpp.org/
Glomosim:   http://pcl.cs.ucla.edu/projects/glomosim/          
NRL's Sensor Network Extension to NS-2:   http://nrlsensorsim.pf.itd.nrl.navy.mil/
J-Sim:   http://www.j-sim.org/v1.3/sensor/sensornets_tutorial.htm
SENS:   http://osl.cs.uiuc.edu/sens/
NESLsim:   http://www.ee.ucla.edu/~saurabh/NESLsim/

Programming ( C, C++, JAVA,  MATLAB,  CTex )

CSDN:   http://www.csdn.net/
Fresh Meat:   http://freshmeat.net/
Math Tool Net:   http://www.mathtools.net/
Source Forge:   http://sourceforge.net/
Java Numerics:   http://math.nist.gov/javanumerics/
C/C++ Users Journal:   http://www.cuj.com/
Programmers Heaven:   http://www.programmersheaven.com/
CTex BBS:   http://www.ctex.org/forums/
MatLab BBS (Chinese):   http://www.simwe.com/cgi-bin/ut/forum_show.cgi
MatLab Forum:   http://mathforum.org/epigone/comp.soft-sys.matlab