There's nothing informal (as I see it) about "At the present time". In fact, I'd argue that it's more formal than the the other three options you present.
"Currently" and "today" are acceptable in your use but I would avoid "nowadays", which sounds very colloquial to me (AmE). This is discussed to some degree on the Wictionary talk page for the word nowadays.
How stylistically aligned is "nowadays"? As a non-native speaker I may be very wrong on this, but my intuition is to avoid this word in business context and use "presently" or "currently" instead. Am I right? 188.8.131.52 20:58, 18 December 2009 (UTC)
That’s right, nowadays would be out of place in a business contract or treaty. It’s too nonspecific and colloquial. —Stephen 02:07, 19 December 2009 (UTC)