That would be me We did the day trip yesterday. The Yamuna Expressway is the way to go. About 3 hours each way from Noida. I actually found it far more scenic than the old road because you are elevated a bit and can look out across all of the farmland. It also take you right past the new F1 racing facility which is pretty cool.

The foreigner ticket Rs. 750 is good for admission to 5 different places if you go on the same day- Taj, The Red Fort, Fataphur Sikri (spelling?), Akbar's tomb and one more place...I don't remember. I've only been to the first 3.

Before a day trip to Agra from Delhi would be VERY ambitious. Now it is totally doable but it is still a long day- beats spending a night in Agra IMO though!