You can find these under the "Exotics" menu, and "Investments" option. The purpose of the investments is to provide different upgrades. You will need at least $1.5 million ($40 million for Montana Legal and $20 million for Montana Sports) to purchase most of these investments. The investments will help you level up faster.

Montana Defense: Carry an extra weapon and maximum ammunition.
Montana Fitness: All your henchmen gain 50% health.
Montana Financial: Launder all of your cash with 0% interest.
Montana Holdings: Fronts will cost you 10% less to purchase.
Montana Legal: Visibility Events reduced by half (cops look the other way).
Montana Productions: Unlocks all of Tony's clothing options in the cheat menu.
Montana Records: Unlocks new music tracks and create a new playlist.
Montana Sports: Maximum bets go up for all your gambling.