Search for one on the play store now that that's an option - I know they're out there.
Ah, I see the Bluecoat K9 web filter is available. No idea if it works on the HD/HD+ but their software client for Windows is pretty good (ie, hard for the folks with kids I know to defeat.)
As Bob points out below, openDNS is a much better solution if you want a security layer and everyone's willing to stop looking at n00d pictures. For per-device, Bluecoat works well in their Windows incarnation.
Are you primarily concerned about home or mobile use? If for home, OpenDNS provides a good "house level" of filtering that you can enable for your entire home network. It won't stop everything, but it does a good job of filtering out malicious sites. They have a base level of service that's free. The best thing about it is that you can set it once, on your home router, then any devices on your home network will get some protection. It's not a full blown content filter, but easy to implement.
If you have access to the Google Play Store, you might like something like the K9 browser by Bluecoat, a reputable content filtering company.
Try NetNanny for Android. I use it on my kid's Samsung galaxy tab. It's great. It does require a paid subscription but it is worth it to me.