Very lightweight, but has tons of features like mass-renamer, filters, tabs, etc.
I always have like 20 tabs opened and the memory consumtion is only about 10 MB.

The icons are not nice, but you can replace them easily (toolbar skinning feature).

Note: I'm not even using the PRO version.

+The first software I'll install in my computer
+Blazing fast & easy to configure (See 381 pages manual)

This is best filemanger what i have used. Even free version is really good, but it is lite with lesser options.
I was going to buy the full version, but i noticed you can get full version for free. Just go http://zabkat.com/trialpay_wall.htm take inkclub instant deal. Order some shit, they send receipt your @mail. Send that to confirm you "buy some stuff". Then you get full license and best part is you dont have to pay those inkclub orders because just leave the stuff into post office. Post office returns those inkclub stuff if you dont gonna get them and pay. It may sound little cheating but i read terms very vell and its 100% legal.

This is one of the best that I have used. It is fast in execution and it's interface make it easy and quick to use. Even the light version is very configurable.