Addict Spell is a very versatile spell checking component. It works smoothly with WPTools, supports undo and 'SpellAsYouGo'. Using the dictionary compiler you can even create your own dictionaries, if you don't find what you need in their large collection of dictionaries.
EDSSpell is a good choice if you need spell check capability in your project. It is fast, reliable and works nicely with WPTools.