Rangers-probably the overall most damaging striker by mid heroic onward. It gets great damage from twin strike (its real striker feature as hunters quarry is barely worth mentioning in the long run). It also possess the best nova of all the classes.
Warlocks-Not as damaging as most it packs a lot of status effects (near controller level in fact some groups use them as controllers) and its curse has awesome feat support. It is often used as part of a hybrid (like paladin|warlock).
Assassins-Tricky. They tend towards lowish damage by paragon onward (they do alright in heroic) and are glass cannons (though this can be alleviated a bit by use of their class features and powers). They also tend towards late damage since the class wants you to put their feature on a target over the course of several rounds and it hard later (while during this time your target could be dead before you use it).
Executioner Assassin-If you want to be an assassin choose this one. This one primarilly uses basic attacks supplemented by a few special at will powers. It has one massive encounter power and uses daily poisons rather than daily powers. It is considered pretty good though not as nasty as some. This class also has decent skills and lots of out of combat utility. In fact you can use your poisons before a fight (by poisoning food and the like) and that can do special attacks on your target and they have utilities that interesting and useful.
Avenger-Double roll is the striker feature which means it is more accurate and more likely to crit than any other class. It also has enough support to get a decent nova and so is one of the better strikers. It is also very tough. One issue is that its feature requires you to not get surrounded by enemies as it only works with a single enemy next to you.
Barbarian-Does alright damage at will (can be made pretty good if you charge). It also has brutal multiattack encounter powers and the daily rages are nice as well. Barbs are masters of breaking encounters wide open due to rampage on a crit. This is awesome but also unreliable since you generally do not control it. Ragebloods are the best strikers of the group (str primary dex secondary con is not as important as dex) and can explode on an encounter with their class encounter power (charge as a free action after killing somebody).
Berserker-Can be made about as nasty as a non-rageblood barbarian and might be better for a certain type of flavor (such as an unarmed desert nomad barbarian). The rageblood barbarian is slightly better pound for pound (only due to the charging encounter power).
Blackguard-Very nice. You don't get a daily at level 1 but you get it eventually at level 5. They can have good damage if they build to charge and can get a decent nova going. They also have great AC and durability (Plate+heavy shield and defender HP) so it makes them among the toughest strikers. Good choice if you want a dark, brutal, and tough guy.
Monk-Among the most mobile. They can deal decent damage on one target but not great. They also lack a good nova BUT they are among the best at spreading damage around. They also get two powers for every power they choose (one for an attack and another is a move type). Best idea for them is to build to be mobile and take powers that allow them to hit lots of targets while having really high defenses (such as five storms for a close burst 1 and taking feats to give better than defender AC). From a lot of feedback they are considered a lot of fun due to their mobility and ability to spread the pain.
Rogue-Deals more damage than a warlock but is also very good at controlling (not quite as good as a warlock though). The warlock, ranger and rogue is the trifecta of damage versus control with warlock as high control and relatively low damage and the ranger is higher damage with less control (rogue is in the middle). They can deal high base damage especially using things like riposte strike and can get a nova going with their minor action attacks. Lots of skills and some good utilities keep them versatile.
Sorcerer-Can be made to deal pretty good damage on one target and can possess a decent nova which is available early. They are more dangerous used as a ranged group destroyer as their striker feature works on area attacks. They can be mostly covered by a genasi wizard (the difference being that the wizard would have better daily powers but the sorc can get a better encounter nova). Sorcs also get some nice defensive utilities that make them tougher than they appear.
Vampire-Highly thematic (and probably the first time in D&D that they made a balanced and usable vampire). It works well for what it is but you get nearly no class based choices (which is fine once but you are not likely going to be building a bunch of different vampires in the long run). They have some decent daily powers and blood drain is nice as an encounter. In order to get a nova you need to multiclass out (even if the power may not get the vampire bonus damage). It is also harder to optimize since it is a shadow class using implements (both are supported less than their counterparts). The class is tough to kill due to regeneration and can actually make the party last longer (since if they are low in HP and you have more surges than they started with in the day you automatically go to full health and if needed you can suck a surge from your friend which you would choose the friend with the most surges thus sharing the wealth and allowing the group to go farther). vampires also get a nice skill list and their utility pwoers are fantastic out of combat (they can use a gaze that prevents enemies from making opportunity attacks but OOC will charm and give you a bonus to bluffing and diplomacy or turn into a bat to get to a high up place) and many are encounter utilities. Low choices and relatively low damage but lots of utility. In some circles many think of this almost as a solo class and less a striker (heals itself, has controlling powers, can have excellent defenses and can take some heat, and has an official striker feature that makes for decent damage).
(Honorable mention)
Bladesinger-I mention it since it is easier to build this as a striker than a controller. If you build it as Str primary and Dex secondary and multiclass fighter you can be nasty. You take a power swap for rain of blows and take the PP shock trooper which also gives you a 3 attack power. On standard turns your striker feature are your blade spells along with the standard charge and MBA boosters. When you nova youuse your bladesinging power and unleash shocking twister and rain of blows. Your damage that set of turns will be massive. On other turns you will use wizard dialies that don't care much if you hit and then make minor action mbas. It will work as a striker in most groups.
(Honorable mention)
Wizard-A Genasi Wizard or Tiefling Fire Blaster can be built to do striker level damage, using the support for the races and the wizard class.