I have used Vanguard Prime and now Vanguard New York Municipal Money Market Fund and have been incredibly thrilled by the consistently high rates and ease of use.

Setting up online transfers to new institutions can be done automatically with some verification. Actual transfers take about 2 days, but that's pretty standard.

The only drawback is that the municipal funds don't yet have AMT-free options but the yields are high enough compared to AMT free accounts that it's worth it.