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:
1Password can import data from many popular applications, including:
AppShelf AutoID Data Guardian1 (formerly Password Retriever) eWallet2 KeePass and KeePassX LicenseKeeper Minefield Password Safe 3 PasswordWallet by S3 Passwords Plus3 RoboForm Passcards and Safenotes SplashID by SplashData TurboPasswords (formerly Cloak) Web Confidential
Highly recommended app, well worth the purchase price. (EDIT) 1Password does not include Linux support at present, just OS X, Windows, iOS and Android.