Even if you have a reliable baby-sitter, you still need a backup plan for sick days and vacations (hers, that is). Sittercity (www.sittercity.com) connects parents in 10 major cities to a roster of qualified college students. You can also post jobs, find a new permanent baby-sitter, and maintain an on-line sitter list for quick reference. You pay $40 for the first month and $5 a month thereafter (not including the cost of the sitter — or the bags of Sun-chips she eats).