# coding: utf-8
from PyQt4.QtGui import QDialog, QVBoxLayout
from qgis.gui import QgsProjectionSelector
new_dialog = QDialog()
new_dialog.resize(800, 800)
layout = QVBoxLayout()
projection_selector = QgsProjectionSelector(new_dialog) # Widget based
layout.addWidget(projection_selector)
new_dialog.setLayout(layout)
new_dialog.show()