A simple way is:
<button type="submit" name="TheButton" value="Oranges">Apples</button>
... but it will break in Internet Explorer (IIRC, up to version 7).
If you have only one button:
<input type="submit" value="Apples">
<input type="hidden" name="TheButton" value="Oranges">
... will work fine.
Otherwise, using server-side logic is the best approach:
<input type="submit" name="TheButton_Oranges" value="Apples">
, TheButton_, . , JS.