Stateline tack is where I started for my bitless bridle-- I bought an all-leather sidepull to try and ended up loving it, but sold it because it was a tad too big on my arab. Tory Harness Leather Nose Side Pull
I have had the best experience, though, buying biothane (what endurance horses use) bitless bridles because they are frequently convertible. And, while you can choose some pretty wild biothane colors, you can also choose a more "normal" shade of brown or black.
For example, my trail bridle is a biothane sidepull, but I can swap out the throatlatch for poll pressure straps if I feel that my horse needs the extra pressure. Alternatively, I can clip on bit hangers when I decide not to go bitless.
I use tayloredtack.com. They also have excellent "S" hackamores if you wanted something with a little nose leverage. Taylored Tack
Neck reining: A horse that knows how to neck rein should neck rein in any bridle, simply because they operate off of where the rein lies on their neck + leg. I can neck-rein my gelding in his sidepull. That being said, a sidepull is designed for direct reining-- hence the name!
I like sidepulls better than, say, bosals because whereas a sidepull attaches on either side of the head, a bosal attaches beneath the chin. I feel that a sidepull gives my horse better direction.
I hope this helps!