There are tons of sites for water plants on the web - it'll depend, to a large extent, on your tank temperature, lighting, partly on your water values and whether you want to run a CO2 system or not.
In my tanks, with no CO2, no heater and a very varying amount of light, the plain old anchor moss and its variants (christmas moss, flame moss) are doing very well. If you look around in local forums, you may even find people who will share out their clippings for little money (moss will grow and needs regular clipping).
A lot of underwater plants won't care about the substrate, since they use it only for mechanical stabilization. Cleaning - I only have snails, so a gravel cleaner for doing a water exchange is all I use. Treatment - the small tank (10 l, that's about what, 3 gal?) in the office gets a pinch of food (for the snails) and a drop of nano fertilizer each workday and a water change every other week. It's still doing well if I do nothing for a couple of weeks (when I'm on holiday), although the snail population goes down a bit during that time (but recovers as fast). The large, thoroughly neglected, tank at home gets a pinch of food whenever I think of it. The moss is still doing well, but we have very loaded (for Germany) tap water here.
On the other hand, check out "dutch plant aquarium" on the web. You can get _very_ elaborate there, depending on how much effort you want to spend on it. Those tanks will invariably need CO2 fertilization, though.