Someone recently pointed out screen to me. It’s incredibly useful. Not sure how it passed me by until now. It allows you to create virtual terminals, which you can switch between easily, so you don’t have to ssh to a remote machine multiple times. You can also detach and reattach screens and programs running in detached screens will continue to run – so you can ssh to a server from work, run screen, run some long-running program, detach the screen, close the connection, go home, ssh into the server, reattach the screen and continue where you left off.
Another random bit of usefulness that came to my attention recently is the \G modifier in MySQL. Just put \G at the end of your query instead of a semi-colon and you get your output in an easier to read, vertical format. Obviously this is a rubbish format if your query pulls back loads of results, but if you just want to look at a couple of records its rather handy.