Eric McKiddle offers excellent suggestions for a beginning pastor's library. These could also serve as gift suggestions for a seminary student (though you have to decide if he already owns the books). They would also be great for anyone motivated to study more.
I couldn't help but add just a couple of suggestions in the comments!
Chris Brauns is the Pastor of The Red Brick Church and the author of Unpacking Forgiveness and When the Word Leads Your Pastoral Search. You can follow him on Twitter @ChrisBrauns.