Yoshi's Island has got one of the most beautiful graphics, even ignoring Super FX stuff. In fact, there is notoriously special background which took me so long to rip (credit me before using it!): The sunset background seen in e.g. 3-1 and 6-1. The reason it's special is because it uses HDMA to break the 2bpp limit (I mean, it is a layer 3 background). Here are some images showing this background:
In fact, it's supposed to be faithful to the original background so parallax, wave effect and palette animation are included.
(But only if you use SA-1 and don't use a layer 3 status bar.)
In addition, I also release the script (or rather an updated version thereof) I used to "rip" the HDMA gradient: Link