General:
* Overabundance: More than enough
* Overact: To act in an exaggerated way
* Overambitious: Having goals that are too difficult to achieve
* Overanalyze: To analyze something excessively
* Overbearing: Dominating and controlling
* Overcast: Covered with clouds
* Overcome: To succeed in dealing with a problem
* Overconfident: Having too much confidence
* Overdue: Past the time when something should happen
* Overestimate: To think something is bigger or better than it is
* Overjoyed: Extremely happy
* Overlook: To fail to notice something
* Overpaid: Paid more than is fair or usual
* Overreact: To react in an excessive way
* Overrun: To spread over an area in large numbers
* Overshadow: To make something seem less important
* Oversimplified: Made too simple
* Overspend: To spend more money than you intended
* Overtime: Time worked beyond the regular work hours
* Overturn: To reverse a decision
More specific:
* Overboard: Too far
* Overcharge: To charge too much money
* Overcoat: A long coat worn over other clothes
* Overeat: To eat too much food
* Overestimate: To think something is bigger or better than it is
* Overexpose: To expose a photograph to too much light
* Overhear: To hear something without intending to
* Overpower: To be stronger than someone or something else
* Overpriced: Too expensive
* Oversleep: To sleep for too long
* Overstate: To exaggerate
* Overtax: To put too much pressure on someone or something
* Overthrow: To remove someone from power by force
* Overwork: To work too much
This is just a small sample - there are many more words that begin with "over-." You can use a dictionary or online resource to find more words.