You've already received some good answers about neighborhoods, but I'd like to add just a little.
First of all, no city is completely 100% safe and you always have to be on your guard.
But don't just take it from me, Ray the Realtor. I spent several years as a Deputy Sheriff in Fontana, Rialto, Bloomington, & Rancho Cucamonga & then more as a Police Officer in Pomona. When it comes to gangs and crime, I've seen it all. When I take buyers out to show homes, the things I look for that many don't notice are the telltale signs of crime. Many times, when buying a home, the excitement can block your view of things that I notice right away. And I use my particular set of skills, education, expertise and experience to help my clients find the right place to live.
Take a drive around at different times of the day and night and on weekends, especially Friday and Saturday nights. Go to the police station and ask to speak with the officer that handles that beat during swing shift. He or she can give you far more insight than anyone else here.
Also, take a look at the following website for more detailed info on crime in this and any other area you may be interested in:
Realtor - PSC - SSIC
Keller Williams Realty