使用.htaccess从URL中删除PHP文件扩展名

I just finished installing a LAMP stack on Ubuntu 12, and have run into an issue with Apache's .htaccess file. I have the rewrite and redirect mods enabled, and the .htaccess file is working (the URI will redirect to 'www' if there is no 'www' present), but no matter what I try, I cannot get it to remove file extensions. I've tried the I just finished installing a LAMP stack on Ubun