Parksabers is good, but they have no sound at all unfortunately. But the level of detail he puts into his sabers is absolutely incredible.
Random Sabers is no longer making sabers unfortunately, which is really too bad, they had some great designs.
Big Yellow Box ive never heard of so i cant really comment.
Vader's Vault does some great work, but if you want something custom, their build log is incredibly long.
From the FX sabers forums, Id also reccomend LDM Custom sabers, pm or email "General Grievous" for information.
Genesis Custom Sabers is run by a fellow going by the moniker "Madcow" he does great work, some of the best in the lightsaber community, and is always pushing the envelope for his custom works. He also has a fairly new line of sabers called the "Ascend" without sound they run about 210$ canadian plus shipping, or 560$ if you get sound, he uses exclusively plecter labs soundboards like the nano biscotte, crystal shard, petit crouton, and crystal focus.
On www.imperialroyarms.com I would reccomend either Corran Horn, or IndustrialAction if you are looking to have a custom build done.
Ive also recently started taking on commissions for others, basing the hilts primarily on TCSS parts, but ive also got 2 other guys and a machinist im working with to develop a readily available line of sabers based loosely on two of the EU characters.
Ive actually started taking on some commissions for custom builds as well. I tend to use the boards from naigon electronics, I prefer the spark and the igniter boards that he has. Its actually a lot of fun building and designing these things.
"Corellians... no wonder the other Jedi didn't want you leaving your system." "The rest of you were just afraid we wouldn't leave anything for you to do after we were done." Luke & Corran (I,J)