Another vote for Elgato Game Capture HD. I've been using it for my TV out article series (see the threads created by me here at MR in the last two months) and it's been GREAT.
For a Mac, it should be preferred. Do NOT fall prey to the cheap Chinese composite capturer knock-offs - they may be around $10..$20, but you will still need to purchase a $30 license for VideoGlide Capture on a Mac (unlike under Windows, where the bundled software is reported to work). And if you don't go the knock-off way, Elgato's old SD-only capturer costs around $50-60. And it's SD only and not HD - definitely less future-proof than the Elgato Game Capture HD, should you go HD some time even if you only have an SD console right now.