At Oms/b in Midtown, my go-to lunch is "Set A." $8.50 buys your choice of three rice balls from a rainbow of options tucked behind glass cases—plus the soup of the day or miso soup.
I've had little luck with the daily soups (the creamy soups were all bland and watery), so stick to the ordinary but tasty miso soup. The exciting part is picking out the rice balls. There are exactly 48 types, prices ranging from $1.50 - $3.25 if ordered a la carte. $3.25 omusubis are excluded from the lunch set—these are the "fancy" ones such as ikura and shredded omelet omusubis. At any given time there are a dozen to two dozen omusubis on display. If the one you want isn't available, just let them know and they'll make it "fresh" batch in a few minutes.
I try to switch it up on every visit; but inevitably, there are a few favorites I often return for, such as the Unagi omsubi, which features thick unagi slices with shredded omelet, and that sweet unagi sauce dripping down the sides. There's a Shrimp Pop Corn with three pieces of shrimp tempura laced in a chili-mayo sauce—a piece of lettuce wrapped around this one, perhaps to make you feel less guilty about all the mayo and fried food in one bite.
Any of the omusubis that use the house-blended mayos are excellent, including the toasty sesame-mayo mixed with gobo (root vegetable) salad, pictured on the left. Three omusubis and a soup doesn't make a big lunch, so if you're a big eater, add on a few of the small "appetizer" dishes. Highlights from this section include Japanese potato salad, mini-croquettes with egg salad, and karaage, all priced around $2. The shop is tiny with few seats, and if you go during lunch rush, make sure you know what you plan to order; otherwise you'll hold up the line in a tight and awkward space.