It’s usual to have difficulties when recording your own ideas to have basic tracks. You can easily record the guitar tracks and bass and vocal tracks are more difficult but it’s possible, but if you want to have a real drum track, not that machine sounding drums, or organ or even string arrangements is not a very easy task. There are some sample libraries but, maybe a better option is the new software released by Cakewalk, Studio Instruments.
The Cakewalk Studio Instruments software is an easy-to-use instrument collection that can be used to jam along the tracks or inside a music editor software (works with almost every software as AU/VSTi). The collection includes drum kits (with tunning and tempo adjustments to fit your song and built-in effects), bass guitar (with multiple electric basses, pickup selector, slide-note tones, 3-band EQ, drive and compression controls), electric piano (with built-in effects like drive, chorus and tremolo) and string section (with bass, cello and violin, attack, release, chorus and reverb adjustable parameters for the string tone and pan and tone controls for each instrument).
All the instruments include patterns for all music styles, key transposing to fit your own creation and can be played with computer keyboard, mouse and MIDI controller. The most incredible thing about the Cakewalk Studio Instruments software is the price, $49.99.