Si is supposed to be the world's smallest mini. There is on the micro minis list at Sequoia Nursery:
Tom Thumb - tiny red buds & flowers, smallest red 6" plant
Tiny Flame - tiny coral to red buds & flowers, 6" plant
also listed as micro minis, these are all at sequoia nursery:
Trinket - rose pink
Linttle Pinkie
Baby Austin - warm pink
Hi - soft pink
Yellow Bantam - soft yellow

Here's the list of micro-minis available from Nor'East Mini Roses. I hear Red Minimo is a nice little one.

I have Bambino and it's a very floriferous little bug. It's blooming full blast in my sunroom, more flowers and buds than anything else has. It is also one of the few that has shrugged off the Great Spider Mite Attack of '07, not looking bothered about the mites and not looking unhappy about a treatment with Neem.

It has been chosen as the favorite in my sunroom several times over by visiting rose admirers.

Cheers,
Michelle

Here is a link that might be useful: Bambino at Nor'East