Just choose from this list http://www.quickonlinetips.com/archives/2006/11/10-best-wordpress-plugins-for-google-adsense/ because we do have different requirement as one might not be good for you but just right for me.
I use a plugin called Easy Adsense in my WP blog. If you just want to enter the code, you can; but also offers many features if you want more control over it. Cannot put the link up as I'm still a new member (see the sparkle!) but a simple search will help you find it.
I heard that there are plugin that change the id of the adsense code and take some of your clicks and impression, is that true?
I have heard that myself. Not sure if it's an internet urban legend; probably not knowing some people I've met around and abouts. But the one I use asks for a percentage based on the number of views to show an ad. 10% is what I'm using, so an ad appears 1 in 10 views. There's also a choice to just have his link at the bottom of the ads which I'm considering...