Thank you all for your comments.

To answer ktreva52's questions, my wife works as well, and gets home about the same time as me. As for the things we've tried/are trying....

every day, when we leave him, we stuff a few kongs with peanut butter and various other goodies. We've also been leaving him new compressed raw hide bones. In a day's time, he manages to completely devour a 1 foot long bone, so now we're leaving nylabones in the crate with him.
We have also taken him through basic obedience school. For 9 sundays in a row, we both took him to class where we learned sit/stay/down/leave it/heal. Mind you, he is a beagle, so he is still only obeying when he really wants to....
There is a new dog park near us, so we try at least twice a day to go there for 10-60 minutes and just let him run and play with his fellow hound. This seems to poop him out for a little while, but definitely not a complete cure (at least not as of yet, anyway).
We have also just moved. We were in a 1 bedroom apartment, so there was little place inside for him to roam. We're now in a much larger place. There are 2 levels, so he spends a lot of time running up and down the stairs. However, when we left this morning, we could hear him screaming from inside.

Thanks again to everyone. We'll keep trying all of the suggestions people list. You are all very helpful.

Thanks for reading so far,