In preparation for Yom Kippur and doing Teshuva I have translated chapter 2 of Rambam's Hilchot Teshuva and compiled a source book of commentaries and sources on and about it. If I say so myself there is some excellent stuff in there (it changed my understanding of teshuva).
You can download it for free from torahlab (there are 2 pdfs).
One of the most interesting sources I found was this Mabit who makes Yom Kippur much easier to deal with (at least in terms of doing teshuva).
Beis Elokim Shaar Hateshuva chapter 12
After we have explained the concept of repentance, which is regret and abandoning the sin, we must clarify that this is not like other mitzvos. Someone who only does part of a mitzvah doesn’t have the reward for that mitzvah, for example someone who only puts tzitzis on three corners of his garment doesn’t have three quarters of a mitzvah, since all four are required, and so it is as if he didn’t do anything at all. However with repentance, even though the mitzvah would not be complete without the components of regret for the past and resolve for the future, nevertheless, regret on its own, without the resolve for the future helps to a certain extent. Similarly, abandoning the sin without regret for the past also does something. We find with Achav that he humbled himself before G-d when he tore his clothes, fasted and wore sackcloth, which appears to be regret over the past. However he didn’t abandon the sin. Even so it helped him, as the verse states “Because he humbled himself before Me, I will not bring the evil during his days…” (Melochim 1 21: 29). We also find with the people of Nineveh that they abandoned their sins and resolved for the future, but they didn’t regret the past. The instruction of the king of Nineveh was “every man shall turn back from his evil say and from the robbery that is in his hands” (Yona 3: 8). It seems that only the robbery that was in their hands still was returned, but that which had been spent already, which is difficult to return,theydidn’treturn.RabbiYochanan goes even further and says ‘the money that was in their hands they returned, but the money that was in boxes, safes or towers they didn’t return’. (Yerushalmi Taanis chapter 2).