Immediate thoughts: Italian Vals, Jungle Val, Crypt Retrospiralis, Crypt Spiralis, Quillwort, Amazon Swords, Bacopa Carolina (stem), Brazillian Pennywort (stem), Anacharis (stem), maybe Ludwigia repens(depends on light, and it would be green). Dwarf onion plant would likely work. There are plenty more.
How tall is your tank, how many gallons, and what light do you have on it? These would be good choices I think in a standard sized 20, and 29-75 gallon; If you have a 10 gallon or 20 long, many of these would likely be too big or tall. Likewise, if you have a really tall tank, as seem to be popular atm, I am not sure if they would get enough light or reach the top to hide your eggcrate.