I you're looking for a quick easy tool to simply help you with arrangements, check this out...

http://www.chordpulse.com/

I like the pure simplicity of it. I didn't even have to read the instructions lol, if you've ever played with the rhythm section on a keyboard you can master this little program in 30min! I find that it allows me to focus completely on chord progression and song structure without even touching an instrument or messing with a DAW. What's really cool is once you've chosen your chords and blocked out your song in pages (intro-verse-chorus-etc..) you can then press play and change tempo or style on the fly. Or, loop a particular section of your song and experiment with different chords. Don't expect great sounds though, it's not designed for that. It even sounds like a cheep casio you would find at walmart lol. However, it exports midi files for your DAW or a real keyboard. Comes with a 14 day free trial, doesn't hog computer resources, no adds, and only costs $29.00.