The options are almost endless, but it depends on what you're after. If you're like me, a barrel band front sight base like those from NECG or Ruger looks the best, and are precise aiming instruments when fitted with a rectangular post blade and a ghost ring receiver sight that can be fitted to the rail. I like NECG's products, but with our depressed dollar, they are expensive, but then so is everything out of the States.
If your preference is an open rear sight and bead front sight on a ramp, NECG can help you there too, offering plain ramps with a variety of inserts, and rear sights that include single or multi leaf express sights, or the more common leaf sight that is retained with two screws. If these prove to be more costly than you prefer, a wide range of sight options are available from Skinner, Williams, and Lyman. I've never had a problem purchasing directly from any of these companies.