"In Case of Emergency" but not THE "Emergency Fund"

How much money is the right amount to have immediately available to you, in case of emergency?

With all of these big b-school expenses on the horizon, I’ve had that question on my mind lately. Like many of you I’m sure, I funnel a great deal of my savings into my ING account, which is not very accessible, purposefully so. I have two other accounts – Bank of America and my corporate federal credit union. My BOA account is the main one I use for direct deposit, paying credit cards and bills, etc., and I feel like I’ve kept it more or less at the right level – I have enough cushion that I’m not worrying about overdraft fees without wasting any interest potential. But the credit union account is essentially just a rainy day account – it’s helped when I wanted to take out a big lump sum for a vacation or a necessary shopping spree without interrupting my BOA cycle, and ensuring I’m always able to pay every credit card bill in full. But how much is too much to have in that account? Should I just move it over to the emergency fund – out of reach? Or should I keep some of those funds handy now that I have more unexpected expenses coming up? Right now, it’s at $1150.

I know it’s almost impossible to come up with that magic number yet, but I don’t feel like I’ve gotten there yet on this one… Does anyone have any principles / rules of thumb they use for how much “in case of emergency” (but not the emergency fund) money to have on hand?”