I think Graphic Converter is the most versatile shareware image editor I know of... in the commercial software market, any of the current popular programs will handle gifs: Paint Shop Pro, Fireworks, Photoshop, (I know there are more out there)... and full-featured programs like those will allow you to create much more than just a transparent gif.
You could always check out tucows.com's download area for gif-only graphics shareware & freeware downloads if you really want a dedicated gif utility.
Making a choice of an image editor means deciding what functionality you really need. If you only go with freeware, you can always change horses. But when you open up your wallet, things get more demanding.
Any gif editor, free or paid, should allow you to choose variour color depths - from a single color up to 8-bit (256 colors). And any gif editor should support transparency. But beyond that point, things get interesting.
The question becomes, what features do you want or need. Some of the things I use regularly:
1. Single color edits to the look up table 2. Weighted color allocations 3. Force exact colors into the index 4. Work with transparency as if it were a color 5. Lossy algorithms 6. Animation
I could live without lossy algorithms - but not the rest of it. And I don't know of any freeware or shareware that offers all this, and I make my living developing websites. So for me, it's Photoshop or Fireworks. I have both, but I'm new to Fireworks so it's not as comfortable.