Last time I used www.sittercity.com and had VERY good luck.
Caregivers unite at Care.com
If you are looking for a babysitter, tutor, pet sitter or even an elderly caregiver check out Care.com.
This site allows users to join and search the network to find the best possible family care individuals through safe and trustworthy options. Users start off by entering their name and address, and then get connected to care givers. A free account allows users to search with limited profiles, but an extended account allows full profiles, background checks and contact information for the family care individuals that suit specific requirements.
Care.com seems like a great research tool for ensuring your family is safe with the caregiver choice you choose. There is a free account, and 3 Premium accounts to choose from starting at $25 for one month of unlimited access, up to $125 for premium 12 month unlimited access.