If you want to do a code review, and you consider all of the existing tools too bloated, too expensive or too limited, then difr might be perfectly suited for you. If you pass difr a diff file (wherever it might come from), then difr will turn that diff file into an HTML file (not unlike GitHub's view of a diff) with an embedded editor for adding comments.
Once you added all your comments, you simply save the file, or copy the entire page in your email.
Download a jar here. Other than that, all you need is Java.
To create a review page for the diff between your working copy and what's currently on HEAD:
git diff | java -jar difr.jar > /tmp/review.html
To create a review page for your feature branch, if you're using git flow:
git flow feature diff {feature} | java -jar difr.jar > /tmp/review.html
Or if that's too much trouble, pass the HTML produced directly to your browser, using bcat, which is what I do all the time:
git flow feature diff {feature} | java -jar difr.jar | bcat
To get help on the options difr accepts, type:
java -jar difr.jar -h