Comment on Koku

Could be a little bit more smooth and flexible, but overall it's a nice little checkbook app, and it's free! (Donationware)

Note that It stores your data in plaintext plist files, so I mount an encrypted DMG in place of it's Application Support folder to keep my data a bit more secure.
I initally came up with this method for use with Cha-Ching, but the script I wrote can be easily modified to work by replacing "Cha-Ching" and "Cha_Ching" with "Cashbox".
More info here: