Just to note that this isn't the login page - it is the Home Realm Discovery (HRD) page.
If you have:
<persistIdentityProviderInformation enabled="true" lifetimeInDays="30" />
set in your web.config, it will only ask you once and then remember your selection for the "lifetimeInDays" number of days.
You can alter the HRD page - there are many references to this e.g.
Customizing Client Logon and Home Realm Discovery Pages
ADFS 2.0 Home Realm Discovery Deluxe
Home Realm Discovery In WIF And ADFS 2.0 By Query String