Tell your boss that you had trouble finding the car keys, which consequently kept you from getting to office on time. If you are married and have children, then put the blame for lost keys on your child.
Car is a machine and machines are unreliable. Use this fact to your advantage by telling your boss that you were leaving the house for office on time, but for some reason, the car was not starting. Tell him that it eventually took a call to the mechanic to get the car working against.
Traffic is an unfortunate and extremely frustrating reality, but there are times when its existence can prove to be a blessing. Your boss will be well-aware of how cars end up getting stuck on certain roads due to traffic. Tell your boss that you had ended up getting stuck in traffic, which is why you were unable to turn up at office on time.
Overslept or slept late
This is a risky excuse to use, as your boss would not appreciate your inability to get up on time and drag yourself out of bed. However, the excuse is so believable that your boss may let you off the hook for your honestly.
Alarm Clock broke or did not ring
A lot of lazy people use alarm clock as a scapegoat to save their skin and save themselves from the wrath of the boss. Just tell your boss that the clock did not go off, or it shut down due to power outage.
Make an excuse to your boss that you had left the house for office on time, but on your way, you realised that you had forgotten something really important at home and therefore were forced to turn back.
This is a serious excuse and should only be made if your boss is not very inquisitive or suspects you of being a liar. He may want to take a look at your car himself, which can result in you getting busted.
Family emergency can come up at any time and on most occasions, you cannot walk away from them. Your boss would surely be well aware of this himself and will therefore not go down hard on you after hearing that you came late due to a family emergency.
If your office has a dress code, tell your boss that you got late because your dryer had broken down and you were forced to dry your clothes at a nearby laundry shop, as you could not possibly come to office in wet clothes.