Always plenty of talk about resource usage and yes, they are limited, but it just comes down to how you wish to use them. I guess this is why some like Unix, they can slice and dice their system s to fit their own work processes, prejudices and so on.
Generally any tool using a GUI will require more resources, not least of all because they require a supporting environment from which they are invoked and subsequently execute. And those environments drag in lots of other stuff that you didn't know you needed or simply don't want. Hence the development of light weight managers that reduce their impact on the system, while still giving the user that point and click experience.
VLC does a job and perhaps is over the top in many scenarios. I was looking form the perspective of remote control and streaming stuff around the house in a 'Radio Bryant' sort of way. It does it but I don't really want to support a graphical environment in all receivers. But then I went off in a different direction and have been playing with XBMC installations for a day or week, the other end of the spectrum. These have shown me that the music can play without inter-track clicks etc. that I was hearing with a Wheeezy system.
I've digressed!
To install any software you first point of call should be the respository for the distro you've installed. Simply put you just run:
sudo apt-get install <package name>
It will go to the official site, seek the pack and install it, offering to install any dependencies too. What is installed is the working, maybe binary, image of the software which has hopefully been verified to run within that release of the OS. In most cases, for Ubuntu say, this is quite robust but as you go to smaller, niche software, whether distro or esoteric package, then that confidence may begin to wane. Simply because the numbers of folk testing and using is so small.
So in your case, I simply tried:
sudo apt-get install omxplayer
and it reported
E: Unable to locate package omxplayer
This is not uncommon, the package name is not always the name of the application. They might have called it 'omxplayer-mp3' for example.
Then, after a quick Google, I saw it was available on github, but this is more agnostic to the distro and may require support libraries that are not provided in the current release, are the wrong version and so on . Hence my mandrolic term - you have to put some work in, or at least be prepared for it.
So install VLC then:
sudo apt-get install vlc
And mpg123
sudo apt-get install mpg123
There's a variant called mpg321, I'll leave that installation to you. You can have both of course, they very similar and appear to exist because of some early licensing clause and lack of development. But running them is the same; open an xtem and type something like:
mpg321 ~/music/Hedonism
and there's text output of track etc and hopefully audio too! So one can ssh from a remote system, and play whatever tracks you wish.
I'd found their names in some Pi-related forum/site as I was looking for simple(r) ways to verify the sound system from the command line with less system running e.g. no display.
Note, that a man page is usually included with the package, so you can type 'man mpg123' to read the manual. But for Pi packages this is not installed, resources presumably. So just type it into Google instead will often get what you want; man mpg123 in Google results in the mpg123 and mpg321 man-pages as the first 2 results.
VLC will play audio although I did hear glitches on the line. This seems to be common, all audio players for the distro did the same i.e not a VLC bug, and fingers were pointed at codecs, ... but the XBMC distro is as clean as a whistle.
You will want to buy the hardware codec(s) for your video ideas. All the home video I've generated that display on our Sony TV (very picky about formats) run nicely on the Pi once the licence is purchased.
And if you want to run a graphical tool like VLC then you might like to investigate:
ssh -X <your Pis IP> vlc
The -X will forward all graphical stuff (its the X11) back to your system i.e. the VLC GUI will pop up in your local window manager (not Windows natively though).
Hope this helps. Good luck.