In my opinion, the first thing you should consider investing in is........a good pair of headphones (surprise!). This is assuming you do listen to music while you work (which I do all the time) and it was 'life-changing' for me :)

With that being said, my suggestions would be:

1) Sony MDR-V6 - costs <$100 (Beware of fakes, buy from a trusted place like Amazon or somewhere)

2) JBL Tempo Headphones (~$50) (For bass lovers)

3) Pioneer SE-A1000 (Elite sound quality, Open type, so others might be able to hear what you're listening)

4) Pioneer SE-MJ591 (Top of the line SQ you will find only with $1000+ headphones). Price approx:$199-$300

Cheers :)