There's a lot of scientific information available about daylilies that have been tested for performance with Rust, Leaf Streak, and Spring Sickness. Keep in mind that resistant ratings do not mean cultivars will not get these diseases. It means that they were observed to get only 50% or less of their foliage affected with those diseases, and thus performed well enough to be considered acceptable garden and helpful breeding specimens. Resistant cultivars were seen to self-recover without any treatment and were found to be presentable for garden display with foliage trimmed to remove (and discard) affected leaves.
Averaged Rust rankings can be found for individual cultivars in the ATP database here. Or, you can search en-mass in the Search by Characteristics page here.
More information about the source of the scores is here.
Scores for the fungus that is associated with Leaf Streak and Spring Sickness are linked here.
Additionally, listed below are daylily recommendations for cultivars that have been tested for both of the fungi that are related to rust, leaf streak, and spring sickness. Recommendations come from a non-commercial home hobby hybridizing garden in a coastal state with temps ranging from 25-105 degrees, marine and desert/sandy soil, and low rainfall.
I'll update recommendations over time, so you are welcome to check back to find more options, and feel free to send a tree-mail if you have questions or feedback about any of the daylilies listed. I'd love to hear from you about any that are growing and doing well in your own gardens!
Daylilies that are, or have lineages that include cultivars that on average tested resistant (50% or less foliage affected) for fungi associated with rust, leaf streak, and spring sickness:
Daylily (Hemerocallis 'Darker Shade')
Daylily (Hemerocallis 'Dil-Robin Nichols')
Daylily (Hemerocallis 'Donna Mead')
Daylily (Hemerocallis 'Handwriting on the Wall')
Daylily (Hemerocallis 'Little Liza Jane')
Daylily (Hemerocallis 'Open Secret')
Daylily (Hemerocallis 'Regal Giant')
Daylily (Hemerocallis 'Tremor')
Daylily (Hemerocallis 'Woodside Ruby')
Updated October, 2014, and to be continued as next summer's blooms arrive ... !