List theme for pidgin?

A simple alternative option, which lets you fit in twice as many entires, is to hide the buddy details of all the entires. Go to Buddies -> Show and then untick "Buddy Details."

There are several plugins which can be used to improve the buddies list, which includes but not limits to:

Autoresize

Buddy list options: included in the Plugin pack

Extended buddy list sort plugin

And you can find more plugins in the Pidgin's official plugin site.

My buddy list have changed since it was originally installed and now it looks like this:

Well, probably not fully improved but better than the original.

Good luck!

Isn't pidgin built on GTK+ ?

if so, you can use GTK themes to change things like font face & size and the interface elements. Something like the Clearlooks Compact theme will make the interface a little smaller so give you more room for the actual information. http://art.gnome.org/themes

Though as already mentioned, best is to use the specific buddy list plugins and disable buddy info to make a more dense list.