The old version of Google Analytics allowed you to export 50,000 keywords by appending the parameter &limit=50000 to the end of the URL in the address bar, then hitting enter, then exporting as .CSV (not .CSV for Excel).
As of this writing Google Analytics just had a major update. When I attempted to export up to 50,000 keywords using the old method stated here, it didn't work.
Yes, you just need to do this this:
Go to: Traffic Sources > Sources > Search > Overview
Select Keyword Dimension from the Traffic Sources area
In the URL, Where it says:
Where you see the 25 part bold in the link above, change to any number you want. This tells Google Analytics how many keyword rows to show.
The decoding for this URL is this:
Another way to do this:
Go to any standard report. In the bottom right, change the number of rows from 10 to something bigger:
That will change the main URL to have the following in the query string:
Change the table.rowCount to something bigger, up to 50,000
That should allow you to export as many as you want.