I have been developing applications based on C# (.net) and Java (J2EE) for the last 3 years.
But now I feel, Java, C# makes you lame (from learning point of view) and yo
Assembly Language.
Start with the Z-80. Then add 'x86. Then try 68000. Then the TI 320 series of DSP. You might also wish to add the Z-8. Just to see how different machines do it.