I generally do shenayim mikra too fast. Here are a few random points worth slowing down and thinking in Rashi (answers can be found in various meforshim):
1) Rashi (20:1) explains that the parsha of parah is juxtaposed to the death of Miriam to teach that the death of tzadikim is mechapeir like the offering of korbanos. Why then not juxtapose one of the many parshiyos of korbanos that appear in VaYikra with Miriam's death -- why is specifically the parsha of parah adumah chosen?
2) Rashi writes (20:12) that Moshe failed to do a kiddush Hashem because he struck the rock instead of speaking to it. Yet Rashi in Parshas Be'ha'alosecha (12:22) implies that it was Moshe's exclamation of "Shimu na ha'morim" that was the sin. Which was it?
3) "VaYishma haKena'ani ki ba Yisrael derech ha'atarim." (21:1) Rashi explains that the Kena'ani heard that Aharon had passed away. Why does the text require any interpretation beyond its plain meaning, namely that the Kena'ani heard that Bnei Yisrael were travelling in their direction?
4) Why does Rashi (21:21) give a reason for Sichon objecting to Bnei Yisrael crossing his territory (namely, he was paid by the rules of Kena'an to keep them out) but Rashi doesn't give a reason for Edom's earlier objection?
5) Rashi (21:35) comments on the pasuk, "Vayaku oso v'es banav v'es amo", that Moshe personally killed Og. The word "vayaku" is written in the plural -- why does Rashi ascribe the killing of Og to Moshe alone?