Anybody know anything about Sun Country Airlines. They are beginning service between MSP and DCA. Are they reputable?

Yes they are reputable. They are a Minnesota headquartered company that specializes in both chartered and more recently scheduled service. If the price is right, I wouldn't hesitate to book with them.

have flown MSP to Seattle with them-an excellent low price airline

One of the perks you get for flying with them is when you leave from MSP you get to leave from terminal 2, which is much smaller and easier to negotiate than terminal 1. Their schedules are more limited but I fly with them on occasion. You can join their flight club and receive promotions also.

Thanks, all!