How about this?

set datefirst 1

declare @basedate as datetime

set @basedate = '20130808'

select

Today = @basedate,

NextMonday = dateadd(dd, 8-datepart(dw, @basedate), @basedate),

MondayAfterNext = dateadd(dd, 15-datepart(dw, @basedate), @basedate)

Happy Coding!!!

~~ CK