Review Board 2.0 introduced support for Markdown-formatted text.
Markdown is a syntax for marking up text. There's a lot you can do with it, from

adding bold text, italics, sampleCode(), links, and more complex things, like:
test:

Item 1
item 2
Item 3

foo


Bullet-point lists


With multiple items


And sub-lists


Ordered lists


Also with multiple items


And sub-lists.


And inline source-code, like:
def my_function(self):
    """Docstring"""
    for i in range(1, 10):
        print i

There's even support for images:

These all work in all multi-line text fields of a review request, on reviews, and on comments.

Very useful for proposing new code!
See our Markdown reference.