Chrome: We've discussed the challenge of making Chrome use the general Google domain rather than .com.au when searching before, but methods for making that change can often be fiddly and may stop working as Google continues to change its services. Here's a simple method that appears to work right now.
Using the .com.au domain does produce more Australia-relevant results, so why wouldn't you want to use it? One answer might be that you're researching trends in the US market. Another could be that you want to test out newly-introduced features that haven't yet been added to non-US domains by Google.
You can always get Google to search using the main site by visiting google.com/ncr, but that on its own doesn't help if you want to use Chrome's own address bar for searches. Google Operating System offers up a new approach which supplements an earlier method we discussed involving editing user profiles.
The essence of the trick is to visit the /ncr page, then close Chrome and relaunch it, which will make Google ask if you want to switch domains. (This is a variant on the trick Google uses to change your search engine if it detects a change in your IP address when you travel.) Hit the post for a step-by-step walkthrough.
Change Chrome's Search Engine to Google.com [Google Operating System]