Some interesting statements concerning Reward in the volume Pirkie Avot (Wisdom of the Fathers):
http://www.shechem.org/torah/avot.html1:3. Antigonus of Socho received the Torah from Shimon the Righteous. He used to say: Be not like servants who minister unto their master for the sake of receiving a reward, but be like servants who serve their master not upon the condition of receiving a reward; and let the fear of Heaven be upon you.
2:1. Rabbi Judah the Prince said: Which is the proper course that a man should choose for himself? That which is an honor to him and elicits honor from his fellow men. Be as scrupulous about a light precept as of a weighty one, for you do not know the reward allotted for each precept. Balance the loss incurred by the fulfillment of a precept against the gain and the accruing from a transgression against the loss it involves. Reflect on three things and you will never come to sin: Know what is above you --a seeing eye, a hearing ear, and all your deeds recorded in a book
2:2. Rabban Gamaliel the son of Rabbi Judah the Prince said: Great is study of the Torah when combined with a worldly occupation, for toil in them both puts sin out of mind. All study of the Torah which is not supplemented by work is destined to prove futile and causes sin. Let all who occupy themselves with communal affairs do so for Heaven's sake, for then the merit of their fathers sustains them and their righteousness endures forever. And as for you, G-d will then say: I count you worthy of great reward as if you had done it all yourselves.
2:19. Rabbi Elazar said: Be eager to study the Torah. Know what to respond to a heretic. Know before whom you toil and who is your employer who shall pay you the reward of your labor.
2:21. He used to say: It is not incumbent upon you to finish the task. Yet, you are not free to desist from it. If you have studied much in the Torah much reward will be given you, for faithful is your employer who shall pay you the reward of your labor. And know that the reward for the righteous shall be in the time to come.
4:2. Ben Azzai said: Be eager to fulfill the smallest duty and flee from transgression; for one duty induces another and one transgression induces another transgression. The reward of a duty is a duty, the reward of one transgression is another transgression.
4:12. Rabbi Meir said: Engage little in business but occupy yourself with Torah. Be humble in spirit before all men. If you neglect Torah many causes for neglecting it will present themselves to you; but if you labor in Torah then G-d has abundant reward to give you.
5:26. Ben Heh-Heh used to say: According to the effort is the reward.
See also :
http://www.torah.org/learning/pirkei-avos/chapter2-19.html