For filtering, try SurfControl WebFilter. I use this at work, and it's great. Blocks access to all the naughty sites, and you can also filter out undesirable extensions.
Not that cheap, but then you need to protect yourself. It's possible someone might well view a site that causes offense to one of your other customers, and then you could be in trouble.
By blocking these sites, you're taking steps to lessen this risk.