.nice-menu-1 {
z-index:9999;
}

If this doesn't work on its own, try adding the following styles

.nice-menu-1 li ul {
z-index:9999;
}

.nice-menu-1 li ul li ul {
z-index:9999;
}

And if that doesn't work out then also try adding

.nice-menu-1 li ul li {
z-index:9999;
}

.nice-menu-1 li ul li ul li {
z-index:9999;
}
.rotating-banner .rb-slides {
z-index: 1;
}
.block-nice-menus{
background-color: #733F49;
}
#block-nice_menus-1{
height: 30px;
border-bottom:#006699 solid 1px;
}
#block-nice_menus-1 ul.nice-menu,
#block-nice_menus-1 ul.nice-menu ul{ border:none;}
#block-nice_menus-1,
#block-nice_menus-1 li,
#block-nice_menus-1 a{
font-size:16px;
font-weight: normal;
background-color: #840000;
}
#block-nice_menus-1 ul.nice-menu li{
border-right-width: 1px;
border-right-style: solid;
border-right-color: #993300;
border-top-style: none;
margin: 0px;
padding: 0px;
border-bottom-style: none;
border-left-style: none;
}
#block-nice_menus-1 ul.nice-menu li#menu-435{ border:none;}

#block-nice_menus-1 ul.nice-menu a{
text-decoration:none;
padding-top: 5px;
padding-right: 30px;
padding-bottom: 6px;
padding-left: 30px;
display: block;
border: none;
color: #eeeeee;
}
#block-nice_menus-1 ul.nice-menu li a:hover,
#block-nice_menus-1 ul.nice-menu li a.active{
text-decoration:none;
display: block;
color: #FFFFFF;
background-color: #6F0000;
}


.item-list ul li h2 a {
color: black;
font:14px/1.5 Helvetica,Arial,'Liberation Sans',FreeSans,sans-serif;

}

.item-list ul li h2 a:hover,
.item-list ul li h2 a.active{
color: #800000;
text-decoration:underline;

}
div.openlayers-tooltip-name  {
color: red;
font-weight: bold;
font-size:18px;
}
#popup {

}
.openlayers-popup {

}