I'm about 280# and I replaced my standard seat with one of these:
Feels odd at first since it doesn't lend itself to "stable" pedaling, but we really don't do much of that, do we? It turns out to be super comfortable and you quickly adjust to pedaling normally.
I should add that I went through 2 Bell big-ass seats in the past year...the big comfy looking one, but those springs and frame just don't hold up and the seat WILL fall apart. This Schwinn seat has no springs and is well secured to its frame. 6-months on, and it's holding strong.
BONUS: my lady parts thanked me!