I have an iPhone 3G on firmware 3.1.3, what is a good jailbreak that will get me cool features?
You can use Sn0wbreeze to jailbreak iPhone 3G, 3.1.3. And it is good to know that jail breaking your iPhone, will cancel your warranty with Apple. For more information on how to jailbreak you can visit http://www.redmondpie.com/sn0wbreeze-3.1.3-jailbreak-iphone-3g-3gs-3.1.3/.
Sn0wbreeze will do that, and all jailbreaks are essentially the same. There is no "good jailbreak".
My kid says try jailbreakme.com from your device.