The best man, along with the other groomsmen, present a collective gift to the groom, usually during the bachelor party. This is the tradition, but each groom and best man may choose to do things differently.
Traditionally, the best man also provides a gift suitable for both bride and groom. This gift is typically presented at the wedding reception and is always addressed to the bride.
It is the groom's responsibility to give gifts to the best man and his ushers. These kinds of gifts are often engraved with the recipient's initials and the date of the wedding, and are usually something simple, yet meaningful like a key chain, silver pen or pencil or cuff links.