Amazon sword: enjoys medium-high light and nutrient-rich substrate, but very non-fussy if you provide those two things. Grows large and lush even without CO2.
Tiger Lotus: similar to Amazon Sword in terms of needs. Grows large and vibrant maroon leaves, even without especially bright light or a specialized nutrient regimen.
Pearlweed: possibly the easiest stem plant I know of. Unlike hornwort, it actually stays rooted at the base of the stem and grows completely upright, instead of trying to grow sideways and sprouting a ton of stem-roots. Can form bushy masses, or be trimmed for an easy carpet.
Subwassertang: grows in bushy clumps and lacks any roots or rhizomes to anchor itself. Excellent for filling in space on the tank bottom or stuffing into bare crevices in hardscape. Grows in a variety of conditions, and though slow at first, it can multiply surprisingly quickly once you have a lot of it.
Anubias: extremely common, comes in a wide variety of shapes and sizes, very hard to kill on accident. They prefer low to medium-low light; bright light will fry it.
Water sprite: grows quickly if given moderate light and nutrients. Can take over tank if you don't trim it back.
Duckweed, redroot floater, azolla, other floating plants: almost impossible to kill (or remove) if given still water and any amount of light. Multiplies extremely rapidly, absorbs a ton of nutrients, and shades tank below; very useful at the start of a planted tank, as they prevent any algae outbreaks.
Crypts: comes in a vast variety of shapes, sizes, and colors. Requires little light, but needs nutrient-rich substrate for their vigorous roots. Tends to completely destroy all its leaves when first planted, but will usually survive and begin growing once its roots are established.
Dwarf Baby tears are really cool if you get them growing well, need co2 to make them peal. moneywart is good for background. javamoss you can glue to wood/rocks for a natural look etc. I have a list of my favorite plants if you are interested