It depends on what your server is for. Some only need bots for moderation, while others need integrations
The best bot for moderation. Assign roles, set ranks, and set automated welcomes
Not as easy to use as MEE^, but offers more customization
Use for general moderaton and setting timers
Integrates Discord with Trello for project management
Pulls from an RSS feed and auto publishes to Discord
Integrates with twitch to show when streamers are live
Tracks recruitment, shows how many people each recruiter has invited
Tracks statistics, who is most active in both voice and text channels
There's a bot for pretty much anything you want to do on Discord
And if there's not - you can make one!
Discord Servers
Guide to Discord Emotes
Discord Communities