http://users.pandora.be/educypedia/education/mathcomplex.htm
http://www.ping.be/~ping1339/complget.htm the places where you will find the complet theory of complex numbers
http://mathworld.wolfram.com/ComplexNumber.html-on this website you can find the most important aspects of complex numbers

history

If you want to know more anbout the history of complex numbers you ought to visit these websites:

http://math.fullerton.edu/mathews/c2003/HistoryComplexBib/Links/HistoryComplexBib_lnk_1.html-where you can find a list of internet resources.
http://www.experiencefestival.com/a/Complex_number_-_History/id/1249265
http://rossroessler.tripod.com/
The history of complex numbers from different perspectives.

http://digitalcommons.libraries.columbia.edu/dissertations/AAI9985857/
A summary of the mist important moments in the history of complex numbers

interactive

http://wims.unice.fr/wims/en_home.html Lessons, references, online calculators, interactive exercises await for you on this website
http://scholar.hw.ac.uk/site/maths/topic1.asp- Plenty of problems and exercises.
http://www.math.uu.nl/people/beukers/voorlichting/CompVis.htm- draw your own complex numbers
http://scholar.hw.ac.uk/site/maths/activity7.asp -> substract complex no

Interactive software for complex numbers:
http://www.mathaid.com/products/Precalculus/index.html

Interactive Fourier Transform Experiment

http://homepages.inf.ed.ac.uk/rbf/HIPR2/fftdemo.htm

Applications of complex numbers in electonics

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/signals/complex/cmplx.html