There are tons of great community contributed projects on Force.com Code Share! I was browsing last week and ran across SQLForce, a command line scriptable tool that provides ANSI like SOQL DELETE, INSERT, UPDATE, SELECT/DISTINCT, and SELECT/UNION commands. The project has been out for a year but I've never heard anyone talk about it so I decided to give it a whirl.
Here are some sample SQL statements that you can run:
SELECT Id, Name FROM Account Limit 10;
SELECT Id, Name FROM Account Limit 10 Output '/Users/Jeff/Accounts.txt';
INSERT INTO Contact (AccountId, FirstName, LastName) SELECT Acct, N1, N2 FROM CustomObject__c;
UPDATE Contact SET MailingCountry='USA' WHERE MailingCountry IN ('United States', 'US', 'United States of America', 'America');
DELETE From Account WHERE Name = 'My Account';
After using SQLForce for about week now I'm in love with it. Here's a brief video of it's features. The install is absolutely painless so give it a try.