When commissioning artwork, music, etc. from freelance artist, is there anything specific, legally, that you need to do to guarantee your rights and ownership of the assets? Is a simple statement from the artist along the lines of, "I hereby transfer ownership of these pieces of art to you," enough?
Supershigi is right, you don't actually need a lawyer. I've been involved in the video game industry since its origins, and I'm also a lawyer certified in the state of California. Over the years I've witnessed cases where a contract written in layman's terms was able to bind parties to an agreement. People often forget that contracts written in layman's terms (provided that they clearly outline the intentions of both parties and specifically outline compensation terms and what not) are not rendered unenforceable just because they aren't filled with legal jargon. When a court evaluates a contract that was drafted in the absence of a laywer (and without use of proper legal language), the contract will be interpreted based on normal use of the language it was written in.
My advice to you if you want to write a layman's contract is to be very specific and comprehensive about what you want. If you want to own the rights make sure that the artist relinquishes all of his rights and that he will never ask for them back. Make sure that the compensation terms are clearly outlined in terms of time as well as money. Write your contract to be as clear and
obvious as possible because the more obvious it is, the more likely the court will interpret it in your favor. And remember, just because your contract doesn't contain legal language, this doesn't make it unenforceable in a court of law.
That is true provided you are a lawyer yourself or you actually know enough about Intellectual Property law to know if a generic contract template you found actually provides all the protections necessary.
You really don't need to be a lawyer or an Intellectual Property law expert in order to do this. As lawyers, I know we like to think that our services are ultimately necessary at all times, but in today's day and age it's getting easier and easier for folks to be able to educate themselves on the language of simple contracts. There are plenty of legal resources available to indies who cannot afford a lawyer, and most of these contracts are boilerplate anyway... as long as the indie is willing to educate themselves on the contract's terms, and as long as they make sure those terms are in line with their expectations, then they will be fine.