If Lookup Icon not visible in Lookup field using apex:inputField, remove standardStylesheets=”false” from apex:page tag. Else use the below CSS

.lookupInput
{
    display: inline;
    vertical-align: middle;
    white-space: nowrap;
}
.lookupInput img
{
    background-repeat: no-repeat;
    margin-right: .25em;
    vertical-align: middle;
}
.lookupInput .disabled
{
    background-color: #ccc;
}
.lookupInput .emptyDependentLookup
{
    font-style: italic;
}
.lookupInput input[readonly]
{
    background-color: #e6e6e6;
    border: 2px solid #e6e6e6;
    color: #333;
    cursor: default;
}
.lookupInput a.readOnly
{
    float: right;
}
.lookupInput span.readOnly
{
    display: block;
    white-space: normal;
}
.lookupInput span.totalSummary
{
    font-weight: bold;
}
.inlineEditRequiredDiv .lookupInput img,.inlineEditDiv .lookupInput img
{
    vertical-align: middle;
}
.quickCreateModule .lookupInput input {
    max-width: 155px
}
.lookupIcon {
    background-image: url(/img/func_icons/util/lookup20.gif);
    background-position: 0 0;
    width: 20px;
    height: 20px;
    background-position: top left
}
.lookupIconOn {
    background-image: url(/img/func_icons/util/lookup20.gif);
    background-position: 0 0;
    width: 20px;
    height: 20px;
    background-position: top right
}