There is more in the p2p world than the Gnutella network (Limewire, Frostwire, …).
A great p2p network is the Soulseek network.
It’s a bit smaller but it’s great for less commercial songs.
If you can’t find a song on Frostwire, try this one.
The best client to connect to the Soulseek network is Nicotine + <insert witty comment about name here>.
It’s in the Ubuntu repository, so you can just fire up synaptic to install it (system -> administration -> synaptic package manager).
After installation you’ll get greeted by this window:
State where you want to put the downloads and incomplete downloads.
After that, go to the “server” tab and create a user name and password.
Press apply and then ok.
Go “file -> connect” and that’s it.
If you get an connection error, pick a new user name.
The program is pretty easy to use, I’m sure most people will figure things out by themselves.
It’s a great network and I especially enjoy the chat rooms by music genre.