Every day thousands of domains expire and go into a pre-release period, where they're not yet available for registration, but can be purchased from the holding company. NameJet (http://www.namejet.com) is the leading aftermarket vendor for a number of the world's largest registrars, including eNom and Network Solutions. By adding the domains you want to your backorder list, you're guaranteed a first shot at the domain names.
If you already have an eNom login with us for your domain names, you can use it to login into NameJet. If you do not, you'll have to create a login.
Once you're logged into NameJet, you can click on My Backorders to add a domain name. You will need to put in a minimum of $70 for the name, which you will only need to pay if you succeed in obtaining the name.