In about two-thirds of all years, the two parashiot Nitzavim and Vayelekh are combined: in the last decade, they have only been read separately three times and the next time they will be read separately will be in three years' 
Vayelekh contains the final two mitzvot of the Torah. 
time, on the final Shabbat of 5772 and the first Shabbat of 5773 (the 15th and 22nd of September 2012, respectively). In the Mishneh Torah, Rambam lists all the parashiot as part of the "Order of Prayers"; he mentions parashat Nitzavim, but not Vayelekh. Apparently, Rambam considered Nitzavim and Vayelekh to be a single parashah.
Parashat Vayelekh contains the final two mitzvot of the Torah. Mitzvah number 612 is the mitzvah of Hak'hel:
"At the end of seven years, at the time of the Shemittah [Sabbatical] year, on the Sukkot festival, when all Israel comes to appear before HaShem your God in the place that He will choose, you shall read this Torah, facing all Israel, in their ears. Gather together [hak'hel] the nation - the men and the women and the children, and your converts who are in your gates - so that they will hear and so that they will learn, and they will fear HaShem their God. And they will be careful to do all the words of this Torah. And their children who have not known will hear and learn to fear HaShem your God all the days that they live on the Land to which you are crossing the Jordan to inherit it." (Deuteronomy 31:10-13)
And the 613th mitzvah, the final mitzvah of the Torah, is the commandment to write a Sefer Torah: "So now, write this song for yourselves, and teach it to the Children of Israel, put it in their mouths; so that this song will be My witness concerning the Children of Israel." (Deuteronomy 31:19)
In the Mishneh Torah, Rambam writes:
"It is a positive commandment, incumbent upon every single Jew, to write his own Sefer Torah, as it says, 'So now, write this song for yourselves' - that is to say, write for yourselves the Torah that contains this Song [the Song of Ha'azinu in the following chapter], because we never write only a part of the Torah. And even if his father bequeathed him a Sefer Torah, he is nevertheless commanded to write one for himself. And if he wrote it by his own hand, it is as if he had received it from Mount Sinai; and if he does not know how to write it, then someone else writes it for him. And anyone who so much as corrects a single letter in a Sefer Torah is like one who wrote it in its entirety." ("Laws of Tefillin, Mezuzah and Sefer Torah" 7:1)
It is surely significant that the two final mitzvot of the Torah are both commandments to transmit that Torah to posterity. Once every seven years, the entire nation gathers to hear the entire Torah being read out in a public ceremony - the ceremony of Hak'hel; and every Jewish home must have a Sefer Torah of its own.
To be sure, in our age of mechanical printing and mass-produced books, a Jewish home is far more likely to have holy books than a Sefer Torah on the shelves - and this is a legitimate substitute:
"Every single person is obligated to buy other holy books from which to study, like Bible, Mishnah, Gemara and Halakha, to learn from and to lend to others. And for anyone who cannot afford to buy both a Sefer Torah and the other books from which to learn, the books that he needs to learn from take precedence. Our rabbis, of blessed memory, said (Ketuvot 50a; Yalkut Shimoni, Psalms 871): 'And his righteousness endures forever' (Psalms 112:3) - this refers to those who write or buy books and lend them to others." (Kitzur Shulkhan Arukh 28:2)
The Midrash tells us that "the Torah begins with acts of lovingkindness [gemilut chassadim], as it says, 'And HaShem God made clothes of skin for Adam and his wife, and He dressed them' (Genesis 3:21) ...and concludes with Him burying the dead, as it says, 'And He buried him [Moses] in the crevice.' (Deuteronomy 34:6)" (Tanchuma, Vayishlach 10)
It seems to me that the mitzvot follow a similar pattern: the very first mitzvah in the Torah is the blessing, "Be fruitful and multiply" (Genesis 1:28), which Rambam ("Listing of all the Commandments", Positive Mitzvah #212) and the Sefer HaHinukh count as a positive mitzvah. The second mitzvah in the Torah is that of circumcision: 
The mitzvot begin and end with God's concern for our continuity.
"Parashat Lekh Lekha contains one positive mitzvah, which is the mitzvah of circumcision, as it says, 'This is My covenant, which you shall safeguard, between Me and you, and your descendants after you: circumcise to yourselves every male' (Genesis 17:10). And this mitzvah is repeated in parashat Tazri'a, where it says 'on the eighth day shall the flesh of his foreskin be circumcised' (Leviticus 12:3). And many other mitzvot are likewise repeated." (Sefer HaHinukh, Lekh Lekha)
There seems to be a direct parallel between the first two and the final two mitzvot: just as the narrative of the Torah begins and ends with acts of lovingkindness [gemillut chassadim], so the mitzvot begin and end with God's concern for our continuity. Our children are our future, the only way that we can survive to future generations; circumcising our sons brings them into the eternal Covenant with God. And the only way to ensure their survival as Jews is to bequeath to them the Torah, to teach the Torah of God to the next generation.