Navicat MySQL GUI for Mac OS X
I've been searching for a nice and clean MySQL GUI for Mac OS X or Linux lately, and stumbled upon Navicat which is quite cross-plattform (Linux, Mac OS X, Windows) and has a bulk of nice features.
I've been creating a bigger database today, and I've to say that I'm quite happy with the product. I'm currently using the 30day trial, but I guess I'll ask our boss if it wouldn't be usefull to buy some licences here for work.
And if you mind paying for a software so you can use an open source database, there's still CocoaMySQL, which is nice and feature-rich too.
Navicat (Product Details) - the Most Popular MySQL Frontend for Windows, Linux , MacOS X