Demon WP is the best stuff I've used for spiders. It's available at most Co-Op locations. It's a powder in pouches that you mix with water, long lasting and absolutely works from my experience although I was far from infested. We had a few brown recluses at deer camp and it completely got rid of them.

http://www.tractorsupply.com/en/store/demonreg%3B-wp-insecticide-in-water-soluble-packets-4-pk