The find command is definitely a good tool to be familiar with. Also, I've done a lot of really wacky stuff with sed in the past. (and sed experience can help you to work with ed and even ex, for those times the system has crashed so hard that's all you've got) (though I don't think I've had that happen since I left Ultrix).
dc and bc are good things at times. Really, I do a whole lot of really complicated manipulation of data with the various utilities, sometimes all in one long pipeline and sometimes in multiple complicated stages. An example of that is where I'll often take a du output, use sed to convert G, K, and M to the proper amount of zeroes (or maybe there's a du option to do that automatically, I forget), awk out the 1st column and print each as "$1 +" with no returns, echo a "0" at the end, and pipe the whole thing through bc, to get a "grand total." (maybe that's a bad example, but the ([do something]; echo 0) | bc is definitely something I've done a lot over the years.
I used to have aliases to call dc to do radix conversion (like echo "2 o 1337 p" | dc to get "10100111001"). (there's also a great .sig line out there that does some kind of crazy dc stack program to print out an ascii message, that I wasted a good chunk of time figuring out on paper to understand how it worked).
Another great trick I've been using for 20 years is dd piped through ssh, to copy a local hard drive image over the net to another machine, or vice-versa (well, okay, 20 years ago it was rsh). (like boot off a live CD, "(ssh remote cat /my/image.dd) | dd of=/my/dev" to rebuild a local drive from a remote backup.
There are lots of other things, way too many to write here. I'm sure there's a website out there somewhere.
Oh, and another great one from the days when I'd get files with untypable characters in the filename -- "ls -i" to get a files inode, then "find . -inum [inode] -exec rm {} \;" to delete that (or mv {} newname to rename it). Not sure I need that much any longer, but at the time it was VERY useful.