Formal:
* 我回来了 (wǒ huílai le): This is the most common and literal translation of "I am back."
* 我已经回来了 (wǒ yǐjīng huílai le): This translates to "I have already returned," implying you've been gone for a while and are now back.
Informal:
* 我回来了 (wǒ huílai le): This is also used informally, but can sound a bit more casual than the formal version.
* 我回来了! (wǒ huílai le!): This is the same as above, but with an exclamation mark to emphasize your arrival.
* 我回来了，我回来了! (wǒ huílai le, wǒ huílai le!): This is even more emphatic, and is often used to express excitement or joy upon returning.
Other options:
* 我回来了，怎么样？ (wǒ huílai le, zěnme yàng?): This translates to "I'm back, how are things?" and is a good way to greet people upon your return.
* 我回来了，我很高兴！ (wǒ huílai le, wǒ hěn gāoxìng!): This means "I'm back, I'm very happy!" and is a good way to express your joy at being back.
Remember to choose the phrase that best suits the situation and your relationship with the person you're talking to.