The ones I've heard the best reviews of are the Finnex Planted+ 24/7 and the Fluval Plant 3.0. I find that lights made specifically for aquarium use tend to be really expensive though so I prefer getting just normal grow lights. I have a this light for my 20 long and it's worked amazingly. Most grow lights come in a sort of magenta coloured light but there are some that are very yellow like my own.
I read somewhere that for low light plants 1w per gallon will do but for plants that need medium to high light 2+w per gallon is ideal. Not sure how true that is though.
On my 150 Gallon which is a 60x24x24 tank I have a couple of Beamswork DA series lights. You could probably get away with a single light on an 18" tank. I just got a Fluval Plant 3.0 on a 75 gallon tank I bought used. I haven't had it long enough, but I do like it so far.