Report documentation

Hi Gurus,

WHere can i get the good online documentation on BEx reports. is there any tutors(pilot) in sdn.sap.com or weblogs.

i would like to learn it. with variable offest, writing customer exit, sap exit, exceptions conditon, and what r all the formulas available..

hope some will give me good link.. not only with help.sap.com but also the other links.

i would apprecita if some one provides me soon.

kind regards

kasinath