This mod will prevent non-op players from breaking and placing blocks on server. This allows servers to be made in survival/adventure mode, but not have the risk of the players going around breaking all of the glass blocks, but still being able to kill mobs, craft weapons, etc.

Here is the code for this mod:

package thut.breakdeny;

import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.entity.player.EntityPlayerMP;
import net.minecraft.server.management.UserListOpsEntry;
import net.minecraftforge.common.MinecraftForge;
import net.minecraftforge.event.world.BlockEvent.BreakEvent;
import net.minecraftforge.event.world.BlockEvent.PlaceEvent;
import net.minecraftforge.fml.common.FMLCommonHandler;
import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.fml.common.Mod.EventHandler;
import net.minecraftforge.fml.common.event.FMLPreInitializationEvent;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
import net.minecraftforge.fml.relauncher.Side;

@Mod(modid = BreakDeny.MODID, name = "Break Denyer", version = BreakDeny.VERSION, acceptableRemoteVersions = "*")
public class BreakDeny
{
public static final String MODID = "break_denyer";
public static final String VERSION = "1.0.0";

@EventHandler
public void preInit(FMLPreInitializationEvent event)
{
if (event.getSide() == Side.SERVER) MinecraftForge.EVENT_BUS.register(this);
}

@SubscribeEvent
public void denyBreak(BreakEvent event)
{
EntityPlayer player = event.getPlayer();
if (!isOp(player)) event.setCanceled(true);
}

@SubscribeEvent
public void denyPlace(PlaceEvent event)
{
EntityPlayer player = event.player;
if (!isOp(player)) event.setCanceled(true);
}

private boolean isOp(EntityPlayer player)
{
if (player != null && !player.worldObj.isRemote)
{
UserListOpsEntry userentry = (UserListOpsEntry) ((EntityPlayerMP) player).mcServer.getConfigurationManager()
.getOppedPlayers().getEntry(player.getGameProfile());

if (userentry != null
|| !FMLCommonHandler.instance().getMinecraftServerInstance().isDedicatedServer()) { return true; }
}
return false;
}
}