One of the best is BulkSignature. This email signature manager is geared for Google Workspace (G Suite) domains and offers full integration, real-time updates and a lot of options for colors, fonts, logos and social media icons. It's got an integrated AI assistant, collaboration tools and an HTML template editor. It also works with iOS and Outlook, so it's good for companies large or small that want to standardize email signatures and manage them centrally.
Another good option is Zoviz. The company uses AI to create custom logos and full brand kits that are customized to your business. It offers high-resolution logo files, customizable social media profiles, letterhead templates and email signature templates. Its drag-and-drop interface and instant access to high-resolution files means it's a relatively affordable and quick way to establish a brand.