Also Showing: Monsters Inc (U) <br></br> Muhammad Ali: The Greatest (15) <br></br> Cool and Crazy (15) <br></br> Just Visiting (PG)

Having conquered the world (and even the curmudgeons of Critics, Inc) with the Toy Story films, the computer whizzes at Pixar Animation have set themselves a slightly trickier task with Monsters, Inc. Whereas Toy Story made a recognisable human environment the starting-point of its comedy, this latest is set in a parallel dimension, Monstropolis, where an élite company named Monsters Inc. collect and use children's screams as a power source. Top scarer Sulley (below), a giant blue fur ball (genially voiced by John Goodman) happens to be pulling an extra shift for his pear-green (and one-eyed) pal Mike (Billy Crystal) one night when a three-year-old girl sneaks into Monstropolis. The plot involves Sulley and Mike attempting to return the child (non-toxic and friendly, contrary to monster belief) to her human habitat before the mistake is made known.

The opening gag – a monster emerging from a closet to scare a child turns out to be a training simulation – suggested that the Pixar people have become too knowing by half, and I waited, cudgels at the ready.

Yet it wins you over by sheer force of wit, whether in Shrek-style inversion (body sprays come in a choice of scent, "smelly garbage" or "wet dog"), sly reference (Monstropolis's flash restaurant: Harryhausen's) or some terrific visual squiggle like the fishbowl-sized contact lens Mike slides over his eye.

The late sequence in which a production line of doors each access an entirely sealed universe has the mile-high surrealism of a Magritte. Vocally it scores, too: Goodman and Crystal riff off each other with charm and purpose, while Steve Buscemi as Randall, the reptilian baddie, provides a splendid counter-point. If not as ingeniously funny as the Toy Story movies, it's an amiable addition to the Pixar canon – or, as the cigar-chomping football agent Eric Hall might say, "monster, monster".

A teaser for next week's Ali, William Klein's documentary Muhammad Ali: The Greatest catches the boxer at two turning points in his career. Klein, an American photographer domiciled in Paris, first secured access to Ali – Cassius Clay, as then – in 1964 during the run-up to his title fight with Sonny Liston.

His camera seems almost to be a jostling participant in this three-ring circus, and catches some priceless moments. There is nothing more sinister than Klein's roll-call of the Louisville syndicate, a bunch of po-faced Southern businessmen who had "bought [Clay] like a race horse", and nothing more eye-catching than the boxer horsing around with the Beatles just days before the fight. (He lifts up Ringo like a rag doll.)

A volatile social climate simmers away in the background, and Klein's serendipitous meeting with Malcolm X on a flight to Miami articulates a groundswell of support for Ali, not just as a fighter but as a spearhead of black consciousness.

Muhammad Ali, turning on the charm at will, is one of those rare performers who could make boastfulness endearing. The way he stands around happily joshing with his bodyguards and trainers is a world away from Mike Tyson and his menacing entourage of goons.

Ali had his title stripped from him in 1969 for refusing to be drafted ("No Vietcong ever called me nigger") yet he shows no trace of bitterness when Klein next catches up with him (now on colour film) in Zaire, 1974, for the monumental "rumble in the jungle" fight with George Foreman. The self-belief remains impregnable, the patter unstoppable – "I'm so mean I make medicine sick!" he tells a delighted press pack.

What's more, he appears to have the whole of Kinshasa rooting madly for him, so much so that it's difficult not to feel a little sorry for Foreman, utterly outplayed in psychological gamesmanship. The one disappointment here is that Klein doesn't film the fight live and relies on stills of the bout; some footage of Ali's famous rope-a-dope ringcraft would have been the cherry on the cake. As it is, Klein's portrait has a marvellous immediacy and vigour, and gives Michael Mann's biopic an extremely tough act to follow.

The last thing you'd think of calling a documentary about a middle-aged Norwegian male-voice choir is Cool and Crazy, but then director Knut Erik Jensen plainly enjoys upsetting expectations. Already a huge hit in Norway, his film is about a place as much as the communal pleasures of music. Berlevag, a fishing village on the north coast of Norway, is buffeted the year round by arctic weather, yet not even a blizzard will prevent these doughty old geezers from standing shoulder to shoulder, beards glistening with frost, to raise their voices in choral union.

The spectacle is strangely moving. Individuals emerge from the group: an elderly gent who fancies himself a swinger, a die-hard politico still defending the Soviets, an agnostic church organist who admits he's "not very good" yet feels driven to play. There's something so modest and likeable about these ageing choirboys that, by the time they prepare to sing at a festival in Murmansk, you're hoping that the conductor's despairing cries at rehearsal ("You sound like shit!") are nerves before their performance takes the place by storm. Long may they warble.

Just Visiting, a time-travel farce, remakes a French-language version (Les Visiteurs) that mysteriously broke box-office records 1993. Jean Reno as the 12th-century knight and his serf (Christian Clavier) are magicked by a wizard's spell to present-day Chicago, where they reprise the slapstick and fish-out-of-water routines that weren't funny the first time around. Some critics giggled along, heaven knows why.