The Eclipse Marketplace is a plugin that gives access to a huge range of additional plugins for LPCXpresso and Red Suite.
To install the Marketplace client, you need to add the Eclipse Juno update site. Add the following update site: http://download.eclipse.org/releases/juno
Once added and populated (this can take a few minutes, depending on the speed of your connection), you can search for "Marketplace Client". Install this client and restart the IDE.
Now, you will see Marketplace Client on the Help menu. Open the client, and search for the additional plugins.