Hey man, I've been using this app called "OnSong" on the iPad for almost 8 years now. I've even made a video and wrote a blog post about it.
Basically this software is HUGE for me. You can type your chord charts on whatever computer you're working on, load it up to your dropbox folder and use this app to download it. INSTANT!
Also, this app allows you to read PDFs and allow you to even TRANSPOSE your chord charts to any other keys for other singers you're working with.