I have tried a lot of the Mac banking apps and every time I come back to iBank. While I don’t use iBank on my iPhone — their new iPad app is really nice. It feels a bit sluggish to me right now, but looks great ((The icon: no, just no.)) and has a lot of functionality.
As a bonus tip (again thanks to Justin Blanton): instead of using the default ‘WiFi’ sync option I setup a WebDAV sync, but since we are talking about financial data I used the excellent CloudSafe service. I highly recommend CloudSafe because of the security it offers and the speed the service runs at — also it is really simple to use.