Clearly you cannot include everly assembly syntax, but ARM is a fairly common teaching languages.

Please add Amazon S3 and Git support & (Beanstalkapp Deployments).

Please add a preview for CSS Styles.

When you tap a word, select handles appear around the word. However, if the word includes an underscore character, it is considered as a word delimiter.

This would be easier than setting a high wrap column number.

Please associate .xslt with xsl syntax definition so it will be recognized by other apps in "open with". Or feature manual extension of list of file extensions per syntax definition.

First of all your app is awesome! Perhaps you could implement arrow keys. I personally don't like selecting a caracter by taping on it. Right and left arrow keys would be fine.

it would be nice, if textastic would support syntax highlighting for yaml files -- see http://www.yaml.org/

Currently it looks like you can update files on the device from their source one by one.  Something to help ease the absence of SVN and other version control solutions might be found in allowing full directory structures to be updated as well as single files.