I have two completely separate Google apps domains. One of them has all of my contacts, and I'd like to make them available to the other Google apps domain account.
Can I do this?
(If not, is there a Google way to synchronize?)
Use the export function to export your contacts, then the import function to do the same. If you have contact sharing turned on within your domain you should be able to export your contact listing from any of the @domain1.com accounts and import them to an account on @domain2.com.
I am unaware of a synchronizing feature that would bridge your two domains. However, you can sync Outlook and Google Apps; it stands to reason that if both of your domains are synched to the same Outlook (or other compatible contact manager) that this would be able to create a one-to-many backend (the manager) that serves up contact information for your Apps accounts.
Here's a link to the install if you're interested in this. I am not sure if you can sync Outlook to two Apps accounts. Should it be the case that you cannot, sync one domain to Outlook, and sync one to Thunderbird, and sync Thunderbird to Outlook.