General:
* Yo! (Informal, casual)
* What's up? (Informal, casual)
* Welcome aboard! (Enthusiastic, welcoming)
* Glad you're here! (Friendly, welcoming)
* Cheers! (Informal, used in pubs or social gatherings)
* Come on in! (Informal, welcoming someone into a place)
More specific:
* Welcome to the club! (For joining a group or community)
* Get in here! (Informal, used to welcome someone to a party or gathering)
* Sup? (Very informal, used among close friends)
* Nice to meet you! (Formal, but can also be informal depending on the situation)
Remember: Slang is often context-dependent and can be used differently in different regions or communities. It's always best to be mindful of your audience and the setting before using slang.