[serious7]

Whats the best headphone I can buy if I plan on using my onboard sound in my desktop? What equipment should I buy along with that? My total spending is approximately 300 Canadian for headphone+any extra equipment,

 

[Mr Joboto]

I'd personally put the AD900 as one of the better 'phones that will still sound good off onboard.
 
By what equipment should you buy - If you mean an amp, don't bother. Your system is only as good as the weakest link in the chain, so you would want to upgrade your soundcard to something like the Asus Xonar Essence STX - in which case you probably won't be able to afford a (new) AD900 with your budget, so maybe consider the AD700/Alessandro MS-1.