For the longest time, you could get these nice looking templates packaged with Microsoft Office. You can even download them from their large database of templates. Almost anything you can imagine, you will find a template for.
Now, Google Docs has templates too. I took a peek there last week and really like what I see. There are some beautiful covers, documents, spreadsheets, letters, fax covers, business cards, presentation templates and labels.
On the personal side, you can also find calendar templates, invites, cards, resumes and stuff for students and teachers. Worth bookmarking.