I am looking for a password manager that is compatible with open-source password database files, such as those used by KeePass (.kdb) or PasswordSafe (.psafe3). Both of those projects have terrible Mac clients - I'm looking for something a little more polished, but can still share password databases with Windows and Linux users.
The excellent 1Password by AgileBits supports import for both of the formats you mention:
Highly recommended app, well worth the purchase price. (EDIT) 1Password does not include Linux support at present, just OS X, Windows, iOS and Android.