Yesterday I was helping a student search for an old annual report. Mergent Online might be a source you haven’t considered but for many companies they have a good historical collection of corporate filings. Search by company name and then click on "Annual Reports." Reports can date back over the last ten years although the coverage varies by company. The "Annual Reports" link usually includes both the company’s annual report to the shareholders and the 10-K filed with the SEC. The same is true for foreign companies - their annual reports as well as 20-F’s (foreign annual reports filed with the SEC) will be available in both the home language and English, if available. Please note that all reports in Mergent Online are in PDF format only.
For U.S. listed companies there is also a link to "EDGAR’ where you will find the first 25 filings made in the last 90 days. This is not a very useful feature because if insiders have been filing form 4's that might be the only type of report you will find.