For Magic's Fifth Edition core set, Wizards of the Coast decided they wanted new art for several of the cards they wanted to include in that set. James Allen was one of the artists they brought in for the set to re-envision some of the old cards. The cards he illustrated for the set were Diabolic Machine, Shatterstorm, Stone Giant, and Stone Spirit.
The Magic: the Gathering cards illustrated by James can be viewed here: (http://gatherer.wizards.com/Pages/Search/Default.aspx?action=advanced&artist=[%22James%20Allen%22]) Note that the gatherer database does not usually show promotional cards. The gatherer can also experience difficulties with links like this. If you are taken to an error page, click on "advanced search" at the top of the screen. Once on the advanced search page, scroll down to the artist search bar, input James Allen, then click "Add," and go back to the top of the page to click "Search." You should arrive at the page linked above.
Note: This is different person than James Edmund "Edd" Allen (1894-1964), an American pulp artist.