The City of Ember by Jeanne DuPrau?
This Time of Darkness by HM Hoover?
There are also postapocalyptic underground societies in Martel's "The City Underground", Galouye's "Dark Universe", and Clarke's "The City and the Stars"/"Against the Fall of Night" (Or was that a domed city? And there was Norton's "Outside", but I'm pretty sure that was a domed city), but I don't think it's any of those...
Oh, and there's Duende Meadow by Paul Cook and Journey Outside by Mary Q. Steele...I haven't read them though.
Last edited by wayrad; 04-16-2009 at 02:28 PM.