You're thinking of an S-Corp.

An LLC in most states requires no more work than a sole proprietorship, unless you choose corporate taxation. If not, gains and losses go on your 1040. The various tax softwares make it pretty easy to deal with. Of course, if you start hiring people, things get complicated fast, but as long as it's just you, in most states it's pretty much like conducting business without incorporating.

Now, if you find yourself having to collect sales tax, things get more complicated, but that doesn't change because your business is an LLC.

Technically, you don't even have to keep separate books. It's a very wise idea to have that separation, however. If the IRS comes knocking you want to be able to document your gains/losses. Failing to do so also jeopardizes any limited personal liability the corporation would afford you, but again, you aren't realistically going to get limited personal liability if you're the LLC's only employee.

Edited to add: Just to clarify, I'm speaking only of the US, and within the US both fees and requirements vary significantly between states.