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For a free MySQL client ... maybe, but if you're willing to pay a little money, I think Querious is better designed http://www.araelium.com/querious/

If all you need is MySQL, the MySQL Workbench is pretty awesome now that it's a bit more stable:

Love Sequel Pro as well but HeidiSQL on Windows is great too. Both have their pluses, not sure which one I like more.

If anyone's looking for something like Sequel Pro but for SQLite, I recommend Base. Sadly, not free.

I only wish I could find a good Mac client for Postgres. pgAdmin III is awful.

I haven't, but they have a full suite of tools.