i have had some trouble with anacharis. it grows amazingly in a 10g that gets about 2.5 watts per gallon...but very poorly in anything less than that. if you have a bright tank, anacharis will grow itself right out of the tank, as i've found.
i have crypt. ciliata that seems to do a bit better in less light than that. in the 10g, it is reproducing and flourishing. in tanks with less light, the growth is slower, but the plants look healthy. it is my understanding that most crypts will grow well in less light and that ciliata actually needs more than most, so any of those might be a good choice.
i have also heard great things about java fern but haven't used any. java moss certainly hasn't been flourishing for me, but there are still little bunches of it in my 10g randomly attached to driftwood and gravel from a very small bunch i added a year or so ago.