I'm sure you'll get some input from other members on this but for me, the only 'forms' I use on a regular basis are my invoice sheets (basic text docs), my bookkeeping system (a set of two, very simple ongoing XL sheets), and my client info sheets/agreements.
I created all of them on my own when I started up, have tweaked them a bit over time, but they're still working well for me.
Oh, and the dreaded quarterly self employment tax forms (the forms themselves are simple and straightforward, it's the amount of money that goes out with them that's painful

)
Other forms I've had to deal with are business registration and that sort of thing, but those are generally one-time deals and are provided by your secretary of state and such.