Off the top of my head...

Scrambler Pistol. This thing is amazing, it can absolutely slaughter any suit in the game faster then anything but an orbital, but it is balanced by 2 simple things. Magazine size, and headshots. Its mag is too small to kill many suits, but you can work around that drawback with skill, by shooting the enemy in the head.
Just to get this through, the ScP has been capable of 4000+ DPS since its release about 2 years ago, but it hasn't been considered very unbalanced yet, because it requires skill to obtain that DPS.

SMG. Its a spray n' pray weapon, and it does its job really well. Its a weapon anyone can pick up and understand immediately, because there is nothing complex about it.
Someone said that it is UP because the Combat Rifle uses less resources than it, they are wrong. The Combat Rilfe doesn't use enough resources if you ask me. The SMG was released first, just because another weapon comes along that is better than it doesn't mean that it suddenly becomes UP, it means that the other weapon is OP.

Scrambler Rifle...almost. This thing is so close to being balanced, that I can't blame CCP for not seeing that it is OP. All it needs is to have its RoF toned down by about 15-25% to cut back on any modded controller abuse that may be happening. That's it. The weapon when used with human hands instead of modded hardware is fine, but it has too much excess RoF. Its overheat and semiautomatic nature keeps its high DPS from being truly OP.

Rail Rifle. This weapon is the best balanced weapon in the game. Its spool-up time keeps it from being used in close quarters, and its slow RoF keeps it from dealing too much damage. It also takes a lot of skill to effectively use it, and only the best players in the game can use it effectively.... Just kidding, this thing needs to be nerfed into the ground. Lol.