If you've been using Dropbox since the wee early days, you might not have noticed the "Getting Started" tab in the web version. Click it, though, and you'll likely get another 250 MB of Dropbox space for "steps" you've already completed.
Lifehacker commenter terheyden pointed out this little gem to us, and for this Lifehacker editor, it resulted in an instant 250 MB upgrade.
Dropbox has a "Getting Started" page that will grant you +250 MB for completing a simple Dropbox tutorial.
If you created your Dropbox account before the "Getting Started" page was around, you are still eligible to get that +250 MB space.
For me, all I had to do was click on the "Getting Started" tab, and the tutorial automatically advanced to "completed," and gave me the extra space.
If you haven't tried out a few of Dropbox's features, like installing on multiple computers, sharing a folder, and inviting a friend (for another 250 MB boost), you'll have to knock those off, but the free bit of space seems worth the minor effort.