I can think of four broad techniques for tackling this issue.
Firstly, it looks to me that you could probably get away with increasing the size of your UI components and copy. Text really needs to be 14px or above to be well-readable anyway, so there are practical benefits to doing this beyond just aesthetics.
Secondly, if you feel a page seems 'orphaned', and the form is an action relating to some other table or group of elements on another page, you might get away with showing the form as a lightbox. It's not great practice to choose UI elements just because they look 'nicer', but if it's appropriate from a UX perspective then it's something you should look at.
Thirdly, you can add secondary content to the page if it helps promote the activity, or provides help or advice. This is what Twitter does on its login pages (below), but be careful not to steal attention from the form itself. In Twitter's case, the bright white UI elements and subtle highlighting around them keep the form the centre of attention.
Finally, you can make the whitespace more interesting. A common technique on login and 'gateway' pages is to show a blurred stock photo background, as in the following example:
Web-savvy audiences (i.e. other designers) might find this a little clichéd, though. Another technique is a simple colour or gradient for a background. Using something darker than the page body again helps draw the eye to the form.
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