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 public domain.
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.
Vocal & A-Capella samples -Some of the singers, request that you contact them first, if you plan on using their voices, for "commercial projects."
Free Sample Packs gives links to many different sample packs, mostly royality free.
Soundbible contains royality free noises and sound FXs.
Fruitytuts gives a lot of samples, instruments, soundfonts and other musical resources for free.
Hyperreal has a library of classic synth and drum synth sounds.
This article on Musicradar lists tens of links to sample packs with hunderds of sound each. All royality-free.
Freepats is a project dedicated to creating a free and open set of instrument patches, in any format, that can be used with softsynths
GeneralUser GS is a GM and GS compatible SoundFont bank for composing or playing MIDI files.
Vst and VSTi resources
Vst4free 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 gives you information and updates about new vst(i)´s and updates about them.
MyVST showcases of free VST instruments and effects. Updated frequently on their YouTube-channel.
14000 free Synth1 presets! From the "Very Random Streams" this zipfile gives you 14000+! Synth1 instruments, and instruction on how to install external banks.
Here are some sites that contain many categories of useful audio creation resources.
KvrAudio contains loads of audio plugins, both free and commercial, and great community forums.
Vst Cafe is a blog about good, cheap, free stuff.
Over time some threads on the Forum also represent a useful resource. This one has a lot of interesting links found by LMMS users: Users-choices
Music making resources
All8's BeatFinder is a tool for BPM finding.
Scales&Chords is a tool for scale-finding, chord-progresions and more.
Attack Magazine Beat-making drum-patterns dissected, explained and shown as sequencer patterns.
HowTomakeElectronicMusic is a website with tutorials, music production tips and reviews. They are often based on FL Studio, but you can use them with LMMS too.
BedRoomProducersBlog too contains tutorials and reviews, and also some news about discounts on commercial products.
Audacity is a great multiplatform program for recording and editing audio.