DD's school seems to use a mix of reading programmes ones of which is oxford reading tree. She also has some Ginn books and others too. She has a mix of books, some longer/shorter and easier/harder than others.
Some of the words she has had so far are:
a, at, the, I, in, it, an, is, and, am, me, my, did, as, he, can, we, into, go, got, get, if, for, on, be, but, you, was, went, his, have, just, to, your, by, only,
(she has her other little book at school with her and I cant remember the words she got last time - they get 3 new words a week to learn)