I-64 and I-65 cross at the "Spaghetti Bowl" near downtown Louisville, KY.
I-69 and I-70 don't technically meet but they do go to Indianapolis, IN
I-70 and I-71 meet in Columbus, OH
I-74 and I-75 meet in Cincinnati, OH
I-76 and I-77 cross in Akron, OH
I-79 and I-80 cross north of Pittsburgh, PA
I-80 and I-81 meet south of Wilkes-Barre, PA
I-87 and I-88 nearly meet in the Albany-Schenectady, NY area
I-90 and I-91 in Springfield, MA

An alert reader also noted that H1 and H2, as well as H3 and H4, intersect in Honolulu, Hawaii. Now you know (if you didn't already) that the Hawaii numbering system is different because Hawaii doesn't match geographically wth the rest of the grid. They'd have to have negative numbers, given that Hawaii is southwest of the grid origin in San Diego!