Use this plugin to autofill the Site ID field by searching for a site domain on your network.

Domain mapping management for WordPress Multisite.

The WordPress Multi Networks Setup plugin allows site owners to create multiple networks based on your WordPress 3.0 network installation.

Domain Check lets you search domain names, check SSL certificates and HTTPS, set email alerts for domain and SSL expiration, and get daily coupons.

Domain Mapping System is the most powerful way to manage multiple alias domains on your WordPress site and map them to any published resource - creating Microsites with ease!