In a previous thread on this board, I read that employees have a choice of where to keep their SIMPLEs. Can anyone tell me more about this? If we want to set up the SIMPLE at Vanguard for example, does the employer have to go along with our choice and still provide matching funds?

Here's what I learned when looking into this for my husband a few months ago. The employee can setup an account with his choice of trustees, however the employer does not have to agree to deposit directly to that account. In that case you would have to move the funds in a transfer after they were deposited into the employers trustee account - you would have to see how much in fees this would cost - might be better to just use the employers choice if they won't contributed to your choice of accounts.
When we were looking, Vanguard didn't offer SIMPLE - might verify this now. We went with American Century, and the employer does make contributions to it.
Good luck-
Pam