Hi, today I was bored so I played around with the serial API's in mac os x and came up with this app http://next-tech.net/usbconnect.zip. The GUI is pretty nice, so far it lets you specify the baud rate, the device path, and the information to send (ASCII only so far). I have tested this app to run a couple motors from my mac and manage them all from the computer. 
Zterm works very nicely as well. I have also listed some sample code that could be used with xcode for interfacing with the arduino. http://web.mac.com/miked13/iWeb/Arduino/ I'm also working on a program for the non code tellented that is designed to work in real basic. This way if you want the arduino to do something you could simple write an apple script to do it or click on the big radio buttons.
Zterm works very nicely as well
But you've got to admit that R2_'s icon beats ZTerm's any time 
I love it.
Never tried zTerm, nice idea on applescript thing post a link when you finish it. I have stopped developing USBConnect, however, if someone wants further releases with certain features just post, I basically wrote it for personal use
Lately I been busy developing a kernel for the intel 32 and 64 bit series... When I had to get input I can't say how much I wished I was coding an OS for a PDA or something using arduino rather than Intel, 2 weeks trying to figure out how to get input and make an IRQ table and you will love microcontrollers, Much love to the micros!.
I also been working on a simple program for arduino that whatever data you send it gets saved into bytes 0 - 512 so memory locations 0 - 13 if 0 has the byte 0 it sets the power for that port to LOW if its 1 then it sets it to HIGH, so as long as you power up your arduino ur program runs off the EEPROM.
I use screen from the terminal...
screen /dev/tty.usbserial T-11111 19200