Learning a more aggressive style

[WastedTalent]

I am a fairly-new poker player who just finished reading the HOH series and enjoyed it thoroughly. However, Dan Harrington is a pretty "tight" player, as he himself will say, and I am interested in reading someone who is a bit more aggressive (or even super-aggressive). Harrington notes that the conservative style is just one of many ways to play NLHE successfully, but that the more aggressive styles require more skill and practice. I also find it interesting that in his examples, the players labeled as aggressive and super-aggressive are almost always the chip leaders. So, I was just curious about this apparently more difficult style of play, and was looking for some good resources (preferably books) on the subject. Recommendations? Thanks.