Classes are in the order I bothered to do them.
SPY
Primary - Silenced Pistol: As long as the crosshairs are trained on a single target, the silenced pistol will charge much like the sniper rifle. It does damage and has a reload time about equivalent to the sniper rifle but cannot crit and actually isn't very accurate over long distances. It will not charge while cloaked.
Secondary - Remote Control Decoy: Throw the decoy projector onto the ground and press M2 to activate it. For 10 seconds the projector will generate a hologram of one of your teammates which you can control. The decoy is indestructable and will attract sentries, however, it has a limited range relative to your location, and while using it you are uncloaked and immobile.
Melee - Electro-Shocker: Hit an enemy with the Electro-Shocker and they will be stunned for ~5 seconds, completely immobilized with the requisite hilarious spasming. After hitting an enemy the stunner must recharge for 10 seconds, during which time you can try to whack enemies with it for pathetic damage.
SOLDIER
Primary - Homing Missile: Yep. It homes just well enough that a Scout could easily avoid it, a class with normal speed can just barely avoid it, and Heavies are probably screwed. But, the Homing Missile has a distinctive look and can be destroyed by any weapon, although the resulting explosion will still damage the enemy team. Also, the Soldier can only load one of these at a time.
Secondary - Proximity Mine: HEY GUYS I HEARD YOU LIKE STICKIES SO I GAVE THE SOLDIER STICKIES. Seriously, though, the Soldier can apply these to any applicable surface but has to touching it to do so, and he can't remotely detonate them; they'll be set off as soon as any target gets too close. Teammates are safe, but the Soldier who planted the mines will set off and get hurt by them. They can be disarmed in the same manner as stickybombs and will not go off if the target is crouching.
Melee - VAL-09 Entrenching Tool: Criticals from behind. No criticals from the front. Watch your head.
SNIPER
Primary - Scoped Assault Rifle: Capable of automatic fire over very long ranges, but its damage is only about as good as the submachine gun. Unscoped, its accuracy goes completely to shit.
Secondary - The Outback: A single-barrel shotgun with knockback like the Force-A-Nature, but greater. Only holds one shot at a time, though. Can be used like the FaN to jump higher.
Melee - Bowie Knife: A very quick melee weapon - possibly quicker than the bat - but with only about as much damage as the butterfly knife. For those weird Snipers who seem to enjoy melee combat.
ENGINEER
Primary - My First Invention: Consisting of a cigarette lighter taped to a can of hairspray, this early product of the prodigal young Engineer can produce a quick puff of flame in an outward direction. The lighter needs to be rekindled after each puff, but it is still undoubtedly useful in certain situations. Like, say, toasting marshmallows.
Secondary - Sentry-In-A-Can: What looks like a can of delicious Bonk! Energy Drink is thrown by the Engineer, and wherever it lands, a Level 1 Sentry begins to build itself. This sentry is separate from the one built and maintained by the Engineer and has a 360 degree field of vision. However, as soon as it constructs itself it begins losing health, and cannot be repaired. The Sentry-In-A-Can costs all of 200 metal, and will be instantly destroyed if another can is thrown.
Melee - Multitool: Builds buildings faster and gets 150% the value of the metal when upgrading and repairing. However, it is incapable of producing critical hits.
DEMOMAN
Primary - Frag Grenades: Grenades of the classic "hand-tossed" variety. These don't explode on contact, but rather after a set time will go off and spray bullets through a rather impressive radius. If you see the enemy throw one of these - or just clumsily dropped yours because you got hit - the best thing to do is duck and hope that the shrapnel passes over, and not through, your head.
Secondary - Grim Bloody Fable: As per wartime safety regulations, the Demoman can only have one of these out at a time. After being launched, this little number will dig itself into the first surface - or enemy body - that it hits, and start beeping loudly. This beeping is a warning to anyone unlucky enough to be nearby that they have 5 seconds to get out of there before the Grim Bloody Fable detonates with the force of four stickybombs. Now that's an unhappy bloody ending.
Melee - Molotov Cocktail: A blissful union of the Demoman's two great loves, booze and explosions. It's so beautiful that he cannot bear to just throw it away, so instead he just hits people with it. This has a fairly predictable effect, i.e. both the victim and the Demoman will catch on fire. For some reason the Demoman can produce an infinite number of these.