Shoots a wad of gum out of a keyhole.
The "useful spell" that Lupin was showing them was undoubtedly the "wasi" part, in this case with a target word attached, "wad." Again we see how important intention is to magic, since the wad was directed into Peeves' nose by intent with the "go there" part of the spell. In another situation, the spell might be "stolawasi" to send a robe into a student's trunk, but it would only work if the student focused his mind on where he wanted the robe to go.
no words used
Causes loud booming noises, sparks, or flashes of light, designed to get people's attention.
Purple firecrackers to get everyone's attention (PS10)
The wizard who performed the wedding ceremony cast a shower of silver stars over the bride and groom at the end (DH8).
no incantation given
Emits red or green sparks from the wand, used as a signal.
Harry's wand spun around by itself and shot gold flames at Voldemort when the latter pursued him after his departure from Privet Drive. Albus Dumbledore later said that this was because during their duel three years before, Harry's wand had taken on some of the power and qualities of Voldemort's wand, recognized him as both kin and mortal enemy, and regurgitated some of his own power back at him (DH4, DH5, DH35).
no incantation given
Emits an animated ribbon from the tip of the wand that spells words or forms numbers
Wingardium Leviosa (win-GAR-dee-um lev-ee-OH-sa)
"wing" + "arduus" L. high, steep + "levo" L. to raise up, levitate
Causes an object to levitate.
In an excellent example of how intention affects magic, Ron used this spell to make a mountain troll's club levitate, then crash back onto its own head, even though the "wing" portion of the spell seems specific to feathers (PS10).
Causes objects to hold more than their outer dimensions would seem to allow.
While not mentioned by name, this magical effect is seen in a number of places in the wizarding world. It would seem that "wizard space" is fairly common, since Molly Weasley didn't seem a bit surprised when their Ford Anglia could hold a lot more people and cargo than it should (CS5).
(On the other hand, Molly Weasley knew that the car "borrowed" by Mundungus for a Christmas Day visit to Arthur Weasley in hospital had been "enlarged with a spell", rather than having been built like that (OP23).)
Cauldrons apparently can hold a lot of stuff. Harry dumped an entire collection of Lockhart's books into Ginny's cauldron, for example. And apparently it didn't get too heavy for an eleven-year-old to carry as a result (CS4).
Harry's invisibility cloak also seems to have this quality, since it can expand to cover several children and a crated dragon, but still can be easily used by a single person (PS14, etc). However, it has limits. When the D.A. was first formed, Hermione pointed out that the invisibility cloak couldn't cover all the members at the same time (OP17).
The magical tents Mr. Weasley borrowed for use at the Quidditch World Cup were considerably more spacious inside than they looked from the outside (GF7). Perkins didn't want them back because his lumbago was too bad to let him camp comfortably, so Mr. Weasley kept them until he loaned one to Hermione, which proved to be very useful (DH14). That tent was later lost during a raid by Snatchers (DH26).