There are multiple charges that could be brought as a result of the scope of the investigation, including money laundering, obstruction of justice, and no doubt a bit of lying to the FBI along the way, an act that appears to have been quite popular among the Trump campaign and administration.
On the point of collusion: collusion...in and of itself...isn't actually a crime. However, there are certainly other crimes that may have been committed along the way, such as violation of the computer Fraud and Abuse Act, conspiracy to commit a computer crime, and the somewhat nebulous conspiracy to defraud the United States by coordinating with Russia.
"Collusion is not a crime, but basically the criminal equivalent is conspiracy," said former federal prosecutor Randall Eliason. "You could have a conspiracy to defraud the U.S. by interfering with our election."
While all the above crimes are serious, the results of any charges will be largely political: will Congress and the public deem any of those crimes meaningful? If Mueller concludes that Trump was only guilty of lying to the FBI, Congressional Republicans will most likely shrug and dismiss it as irrelevant (don't get worked up over the hypocrisy -- you'll just upset yourself). Violation of computer fraud and abuse is somewhat bigger, but still nebulous and the public will most likely not call for heads to roll. Conspiracy against the United States is better yet, but still rather nebulous. The truth is that for any meaningful result to come out of the investigation, Mueller will need to prove crimes that the public at large can wrap its head around -- crimes that can't just be spun as "process crimes." Obstruction of Justice is one, as abuse of power is something most people can understand. Even more meaningful is money laundering. That's straight-up mob stuff and the public is going to understand that one very well. I'm in the camp that believes that if something ultimately takes down Trump, it will be that one.
Collusion is not a crime by itself. Here are the charges Mueller could be exploring. - Chicago Tribune
Trump is also violating the Emoluments Clause in open sight, but that's extremely unlikely to fall within Mueller's purview so I wouldn't bet on seeing any results on that front.