From LMMS Wiki
These are some pages where you can find samples for your projects. Remember that samples can be copyrighted. It is up to you to make sure that you can use the samples royalty-free in your projects. Public domain samples are not subject to copyright protection, but make sure that user-added content is publick domain.
homemusician Homemusician is a huge collection of samples, soundfonts and useful articles on making music. A search option is placed on the right sidebar.
BcMan's Samples These drum sample packs are royalty free and can be used in your music production. They will work in most music making programs including FL Studio and LMMS. Each ZIP file contains 20 single hit 16-bit WAV samples.
Freesounds The Freesound Project is a collaborative database of Creative Commons licensed sounds. Freesound focuses only on sound, not songs. This is what sets freesound apart from other splendid libraries like ccMixter. New to this site? Read the What is Freesound page to learn more!
Sample Share Samples, Articles and tutorials. User generated and user uploaded content.
homemusician Homemusician has a wide variation of sf2 patches
Freepats Freepats is a project to create a free and open set of instrument patches, in any format, that can be used with softsynths
GeneralUser GS GeneralUser GS is a GM and GS compatible SoundFont bank for composing or playing MIDI files.
Vst and VSTi resources
vst4free This site has tons of vst(i)´s in their library, and with a brief description and star rating on each sound or program you should be able to find what you like.
Vst Planet Vst Planet gives you information and updates about new vsti(s)´s and updates about... updates of vst(i)´s.
Here are some sites that contain many categories of useful audio creation resources.
kvrAudio kvrAudio contains loads of audio plugins both free and commercial and great community forums.
HammerSound Hammersound is a website focusing on computer music and creation of sounds.
Vst Cafe Vst Cafe is a blog about good, cheap, free stuff.