For a true, bright yellow tomato, Lillian's Yellow Heirloom is the one to try.  While barely known in the commercial world it's a favorite of heirloom tomatophilies.  The beautiful beefsteak fruit weighs at least a pound with a flavor that is spectacular.  Very meaty tomatoes that have very few seeds while still being juicy and absolutely delicious. Considered one of the finest tasting yellow heirlooms and unique for its pale yellow (not golden) color.  The only downside is it is a very late season variety, but it is well worth the wait.  If you love yellow tomatoes chances are you will love this one.
 
COLOR: Yellow
SHAPE: Oblate
SIZE: Large
PLANT TYPE: Indeterminate
LEAF TYPE: Regular
SEASON: Late