Awesome start :)

As is always the case with new contributors, there are style issues that need to be fixed. No big deal and they should be quick.

Can you provide a screenshot of how it looks right now? You should be able to add it to the review request.

There should be a blank line before this import.

Imports are in three groups, each separated by a blank line: 1) Python-provided modules, 2) Third-party modules, 3) Project modules.

Can you put all these in alphabetical order?

Might be nicer to import token, and use token.String, etc.

Can you move this to a diffviewer.filters?

Since our constructor doesn't do anything, we can actually leave it out.

Spaces after each ","

Also, functions should always be lowercase, with '_' between words. So, check_line.

Make sure the line is less than 80 characters

Same rule with variable names. spell_checker

Spaces on both sides of "="

Blank line between these.

The indentation looks wrong.

We should probably define a new token type: SpellingError. Then we can highlight that separately.

I think you can do this with:

    from pygments import token

    ...

    SpellingError = Token.SpellingError
    token.STANDARD_TYPES[SpellingError] = 'spellerr'

I haven't tried that, but it might work. We'd need a CSS rule for it, though, but that's easy.

Blank line between these.

Blank line between these too.

Trailing whitespace.

Trailing whitespace.

We want both. codetagify should remain.

This looks awesome :) I'm so excited about this.

A few things to fix up. Only one of them is a tough problem, the rest are easy changes. I'll give the localization thing below some thought... This must be a solved problem.

"A Filter"

Shouldn't need this, since it'll fall back to the parent __init__.

First line, immediately following the """, should contain a one-line summary, followed by a blank line, followed by a description.

So this is an interesting thing I didn't consider. We're defaulting to "en", which probably isn't sufficient for all cases. Imagine a Japanese or French developer putting up code and seeing spelling errors everywhere. We'll need to figure out a solution for this. Tricky.

Extra blank line at the end of the file should be removed.

I'd say probably just .spellerr. Also, it should go in syntax.css.

Two spaces for indentation.

Oh, also, you'll need to add pyaspell to the dependency list in setup.py. Figure out what the latest version is and do: pyaspell>=the_version (assuming 'pyaspell' is what you easy_install).

This doesn't really fit in the block, with regards to the try/except and comment.

Since you're providing spellerror yourself, I'd just pull this line out of the block:

lexer.add_filter('spellerror')
try:
    # This is only available in 0.7 and higher
    lexer.add_filter('codetagify')
except AttributeError:
    pass

Remove this line (enchant and pygments are both "3rd party" modules and go in the same block of imports).

Add a space between the comma and filters

Python lets you do this in one line via a "list comprehension"

spell_errors = [err.word for err in spell_checker]

Since this is both fetching a tuple and returning that same tuple, you can just iterate over a single value without unpacking it:

for val in self.check_line(ttype, value):
    yield val

I'll delete this blank line.