Bacopa is easy, a very fast grower with low light demands. :) My dwarf sags ended up dying, meh--I think it's because I had them right under my t5HO lights, so they stunted and eventually I got annoyed and moved them and they never recovered. My favorite plants are stem plants like bacopa and rotala rotundifolia, they're very forgiving, grow in a range of different light, and with one small batch of cuttings you can eventually fill a whole tank from simply pruning it and replanting the new cuttings.
Since you're a beginner with plants, I wouldn't go the soil route--you can use regular inert gravel with root tabs or you can use an enriched gravel made for planting in like Flourite or EcoComplete (what I use). Very easy to clean, and if you like to move your plants around, or have bottom dwellers or fish that like to dig around, then you don't have to worry about the substrate being agitated and clouding the water.
Oh, and if you're planning on doing a lot of planting in the future, one of these: http://www.fosterandsmithaquatics.com/product/prod_display.cfm?c=3578+3746+12038&pcatid=12038
will quickly become one of your very best friends. I can't imagine life without them now.