Total Commander

For an old DOS geek like me, Total Commander is indispensable - this has to be my favorite utility ever. It resembles and mimics good ole' Norton Commander that made DOS so easy to use. TC is shareware and well worth the $32 investment.
For those looking for Open Source (a.k.a. freeware) Gnu Midnight Commander is the Linux answer for Norton Commander users. There are even a couple Midnight Commander variants that run in Windows (here and here) which work fine from a command prompt. Neither has been updated in a while...