Online Simulator:
http://www.edaplayground.com/

Tutorials:
http://www.asic-world.com/verilog/first.html
http://www.asic-world.com/verilog/syntax.html
http://www.asic-world.com/verilog/operators.html
http://www.asic-world.com/verilog/vbehave.html