Cukiernia Wierniccy/Piekarnie Ambroziak
119/125 Aleja "Solidarnosci" (at Aleja Jana Pawla II)
I'm a sucker for pastries. I went in and got a (3.75 in) fruit tart, to go, for zl. 4 ($1.03). Yummy.
I don't know if this place is particularly noteworthy compared to other pastry shops in Warsaw, but I liked it. And it's certainly easy to get to, as it's at the junction of two major tram routes.
(It does amuse me that "the corner of Solidarity and John Paul II" is an address that would not have existed in Warsaw before 1989.)