What is more important with live plants is the proper lights-most live plants failures are related to the wrong color temp when its not related to non-aquatic plants, improper planting or photoperiod....
Without the correct color temp of lights (kelvin) most species of plants can't photosynthesis or use any ferts added to the tank...
For live plants you want light bulbs in the 5500-6500k range-watts can vary based on tank size and what the light strip is graded for.
Light penetration is also important-often the partition between the lights and water either needs to be removed or cleaned on a regular basis.....
Now there is ya some "Golden Nuggets" (of info) you can hang on to and live by! I couldnt have said it any better or added much to it. Gotta love seeing a post that great on a forum!
For your situation some of the best plants you can get would be anubias and java fern. But they are foreground plants. You would want to line the back of your tank with tall plants. Anarcharis, hornwort, and Bacopa sp are good plants to go back there; this is also a good place to put fake plants. To top it off you could add a floating plant like water sprite or duckweed.
You can probably find anubias, java fern, anarcharis and Bacopa at Petsmart. If you have a Petco in your area it might be worth it to check them out, too.
Yet more good words of wisdom. Both Anubias and Java fern are excellent plants that give you a lot of aquascaping options at your disposal. The floating plants are also very nice and fish love to hang out under them in many cases, just make sure the overhead canopy doesnt get so thick that the plants below cant get adequate lighting.
The only thing I will add to either of these great replys...Is that I very much prefer the substrates designed specifically for planted tanks as opposed to most other substrates available. They come in rusty brown and black and can look quiet attractive. For a 10 gallon tank 1 x 15.4 lbs bag of SeaChem Florite will do nicely. For the 20 gallon tank I think that 2 bags of Caribsea would work out nicely. The first retails generally in the 20.00 range and the smaller bags of Caribsea retail for about 17.00. These both make for a great medium for rooted plants and both will add trace elements to the water for the plants to take up, helping them to thrive. Are these substrates neccessary? No, but I like them, have had great experiences with them and highly recommend them.
Irregardless, good luck with the new project and definitely post pics to let us know how the project progresses!