Harry's First Year letter was an invitation to Hogwarts signed by Professor McGonagall;

Dear Mr Potter, We are pleased to inform you that you have a place at Hogwarts School of Witchcraft and Wizardry. Please find enclosed a list of all necessary books and equipment. Term begins on 1 September. We await your owl by no later than 31 July.

Yours sincerely,

Minerva McGonagall
Deputy Headmistress

It also contained an extensive list of items he'd need to acquire before joining which included a wand and a familiar.

The sole mention of his Second Year letter is in the following passage.

‘Letters from school,’ said Mr Weasley, passing Harry and Ron identical envelopes of yellowish parchment, addressed in green ink. ‘Dumbledore already knows you’re here, Harry – doesn’t miss a trick, that man. You two’ve got them, too,’ he added, as Fred and George ambled in, still in their pyjamas.

For a few minutes there was silence as they all read their letters. Harry’s told him to catch the Hogwarts Express as usual from King’s Cross station on September the first.

There was also a list of the new books he’d need for the coming year.

The list of books included Miranda Goshawk's 'Book of Spells, Grade 2' and a wide variety of Gilderoy Lockhart texts

Harry's Third Year letter was seen in full, but the attached list of books and permission form were not;

Dear Mr Potter, Please note that the new school year will begin on September the first. The Hogwarts Express will leave from King’s Cross Station, platform nine and three-quarters, at eleven o’clock.
Third-years are permitted to visit the village of Hogsmeade at certain weekends. Please give the enclosed permission form to your parent or guardian to sign.
A list of books for next year is enclosed.
Yours sincerely,
Professor M. McGonagall
Deputy Headmistress

We know from later mentions that the book list included the "Monster Book of Monsters" and "Unfogging the Future" amongst other texts.

No mention is made of a Fourth year letter or a book list.

Harry's Fifth year letter confirms the start date of term. There's also an addendum with two additional books;

‘Booklists have arrived,’ he said, throwing one of the envelopes up to Harry, who was standing on a chair. ‘About time, I thought they’d forgotten, they usually come much earlier than this …’

Harry swept the last of the droppings into a rubbish bag and threw the bag over Ron’s head into the wastepaper basket in the corner, which swallowed it and belched loudly. He then opened his letter. It contained two pieces of parchment: one the usual reminder that term started on the first of September; the other telling him which books he would need for the coming year.

‘Only two new ones,’ he said, reading the list, ‘The Standard Book of Spells, Grade 5, by Miranda Goshawk, and Defensive Magical Theory, by Wilbert Slinkhard.’

Notably, Ron and Hermione's letters contains a confirmation that they'd been made Prefect and their badges.

Harry's Sixth year letter is tersely mentioned;

The day after this rather gloomy birthday tea, their letters and book lists arrived from Hogwarts. Harry’s included a surprise: he had been made Quidditch Captain.

‘That gives you equal status with prefects!’ cried Hermione happily. ‘You can use our special bathroom now, and everything!’

For obvious reasons, Harry didn't receive a Seventh Year letter.