Yeah, I was actually working on a disassembler a while back, but my computer crashed and I no longer have the source for it. When I was working on it, the main thing that I wanted was to be able to disassemble X amount of lines at a time at whatever location in the ROM I wanted without having to go through a command line interface that is hard to understand anyways. So I started working on one with a GUI, and it was going really well, in my opinion. At least it worked for what I wanted. Here is the only version I still have access to:
http://www.freewebs.com/the_bott/DisasmTest2.rar
And it actually works pretty well. I'm pretty sure the documentation explains most of what you need to know to use it. Basically you specify the file path of the ROM, what byte within the ROM you want to start disassembling from, and then what the PC would be in that location when that bank is actually being used. There are some other options like changing ".db" statements to ".data" or whatever you want as well as changing the comment symbol. By default they're both set to ".db" and ";", but if your assembler accepts something different for each one you can change it to whatever you want. You could even have it put "banana" instead of ".db" every time data is defined. Like I said before, this is more of a line-based disassembler. So you specify the amount of lines you want to disassemble per "step". That's every time you click the "next" button basically. You can have it disassemble 200 lines at once if you'd prefer, or just 1 if you'd like to see it line at a time. But one of the other things I really like with this is you can use a CDL file created by FCE to indicate to the disassembler what is code and what is data. I even included a sample of that with the disassembler.
You'll also notice there are 3 text boxes it outputs disassembly to. There's one that's assembler-friendly, one that's "informative", and one that's data only. The Assembler Friendly and Data ones are pretty self-explanitory if you look at them. The "informative" one is supposed to provide more detailed information about the disassembly, but it currently only shows the PC next to every line.
But yeah, I actually really like using this disassembler. It might only be because it fits my needs; I don't know if anyone else can make use of it but I can't imagine it's completely worthless so I thought I'd throw it out there. And since it's not the most recent version (the one that crashed with my computer) there are definitely things missing, like label support and a couple more options. It's also not very fail-safe, so if you try to disassemble beyond the end of a file it would crash. If I can recover my old hard drive, then I think I'll keep working on it because with a few more features I think it could be really good.