roggie

WordPress posts and pages can contain Smart quotes and other fancy characters. But Smartquotes and other special characters don’t work properly if you send the contents of a post by email. This plugin cleans up text so it can be emailed properly.
Instead of using this plugin you could use WordPress filters to reformat text, but WordPress filters cannot be used with PHP functions like strip_tags. If you use a filter to remove Smart quotes you can’t also use strip_tags to remove HTML.
Also, WordPress filters don’t remove all the characters that could cause problems. For example, double spaces are not removed properly by WordPress, and Europeans will have problems with the UK pound currency symbol.
This very simple plugin removes all sorts of special characters, including double spaces and currency symbols that WordPress filters don’t manage.
It also has an option to remove HTML.

Cleanup Text

Function to remove smart quotes, HTML and other special characters from text. Call the function with text as argument, function returns clean text.

SaltedStone

All of the other plugins that I have found only replace the smart quotes after the content has been saved to the database.
This plugin will actually replace the smart quotes before it gets saved to the database.
What does that mean? It means that you will now be able to perform better searches for content without having to worry about those annoying smart quotes.
Not only does this plugin fix smart quotes, it also replaces the ™ (c) and (r) symbols into proper HTML entities.
If you find this plugin useful, please give it a rating.

Smart Quote Fixer

Automatically remove smart quotes from post content and titles, before it gets to the database.

Cleanup Text vs Smart Quote Fixer