Miranda IM is a popular windows chat client that is free, fast and compact for embedding multiple chat accounts. Miranda addons are also available that will enhance the features of this light messenger client.
Anyway here are some attractive Miranda themes and skins from deviantart that can be replaced with your default Miranda skin. Though I found all the three skins good looking but if you have any of the theme then do mention about it here.
Download the skins and unzip them. Now copy them to the Skin folder in Miranda which is located in program files.
Ex: C:Program FilesMiranda IMSkins
Restart Miranda client, browse the theme for the effect to take place.