Dehumidifiers make a huge difference. Also, if you have a crawl that has gravel, you may want to consider having concrete laid or resurfacing it. Check any sewer gas pipes to make sure that the standing water isn't the culprit either and you can go to your hardware store to find something to pour down there to remove the smell. Also, if your walls are exposed and unpainted, you may want to consider painting them.
My husband and I fixed up an old, scary basement in a 100 year old home. We did all of the above, minus the "crawl space" area because there wasn't one, and were amazed at the results - smelled much better, walls were sealed. Made a huge difference. But..... was A LOT OF WORK! More work for us because we had to empty it, first, so... now may be the time to do it.