Intellectual Property Clauses
Such clauses may state that the employer owns all intellectual property rights for any creative work produced during employment. If this is something that is important to you then make sure all vagueness around the definition of intellectual property and creative work is clarified and/or removed.
As programmers we write a lot of code and it is important to clarify before you start employment who ownowns the intellectual rights for a new algorithm or any patentable piece of code that you make come up with during your employment.