I suspect that this list is affected greatly by climate. I consider caladiums to be dirt easy here! You have to wait until the soil is thoroughly warm, but other than that, they're extremely easy to grow, though not winter hardy.

Other easy ones for my zone 7 garden:
zephyranthes
crinums
gladiolus (especially byzantine)
pineapple lilies
elephant ears (SO easy they can be invasive. Be warned.)
hippeastrum
lycoris radiata
tiger lilies
canna
gloriosa
asiatic lilies
calla lilies

Difficult:
dahlias (in general. There are a few exceptions.)
oriental lilies
crocosmia (getting the right cultivar is key)

virtually impossible:
tuberous begonias

I'm a sucker for all Amaryllids, but I grow mine in pots, mostly indoors.

Cannas and Glads are super easy to grow, but are not on my "must have" list because I despise digging and storing for winter.

One of my favorite tender bulbs is Habranthus or Zephyranthes, commonly known as Rain Lilies. They look fabulous grouped in pots, and for me, they bloom shortly after being thoroughly watered in summer. I grow them in my east facing window. I currently have a pot of light pink ones, but I'm on the lookout for yellows and whites, too.

Another beauty is Sprekelia... though not always easy to locate, they're worth growing for their lovely red, odd shaped flowers. I use them in my Amaryllid breeding program.

For eye-popping color and shape, Scadoxus can't be beat! The most common variety, multiflorus, may take a while to get going, but once they bloom, they look like little firecrackers going off! A most awesome bulb!

Ixia and Sparaxis are nice flowers, easy to grow... as is Acidanthera.

This is the first year I'm trying a Pineapple Lily, and last year I grew a lovely dwarf white Calla.

Most any tender bulb can be potted up and grown in the north... just bring it in before it gets cold, and treat it like a houseplant over winter. If they're resting, water very sparingly.