LMMS also has its own percussion synth.
As for samples, Echo Sound Works sends out occasional freebie packs on their newsletter. Their samples are usually good.
Black Octopus Sound has a huge sampler pack that you can use in commercial stuff.
Also keep an eye out for SFX packs around GDC (Game Developers Conference). Sonniss publishes one every year. You can probably find the (legit, official) torrents for past years.