@IL
you can add a widget to an item. So just create a for example frame that contains your icon and add it to the list item.
QListWidget *list = new QListWidget(this);
//...
QFrame *custom = new QFrame;
//add whatever you need to the frame
QListWidgetItem *i = new QListWidgetItem;
list->addItem(i);
list->setWidgetItem(i,custom);
I used this for a list where each item needed several buttons to get for example detailed information about the item or delete the item from the list with one click