When I want a trailer in a planter, I use either petunias or asarina. I prefer the asarina but haven't had it for a few years. I bought the first seeds from T&M but I've noticed that they now have them in nurseries here.

I was thinking scaveola, but when i looked at a picture i had from last summer, it doesn't trail quite so much as just mound out. Was pretty, though! :)

You could try diascia(looks sort of like trailing snapdragons). I've had good experiences with this one. Probably won't get as big as you want though.

I planted "Summer wave- blue: torenia" which has really goregous(IMO) flowers that look like little horns. It says that it is for part shade-shade but I didn't read the tag very well and bought it even though I only have full sun for my pots. As long as it doesn't dry out, it looks great in full sun. On the down side, it really isn't bushy at all. It'll trail down a long ways, but if you want bushiness as well as trailing, don't pick this one.

My go-to favorites for trailers are superbells- Calibrachoa. But they look like miniature petunias, so you may not like them. You know how lots of tags say "deadheading not necessary", but if you don't deadhead, they have long stretches where there aren't really any blooms? Not these ones! They seriously bloom non-stop from spring until frost.

I don't really recommend Sutera cordata(bacopa). It is pretty well impossible to deadhead because the flowers are so tiny, so it has breaks between blooming(depends on how constantly in-view the planters are I guess). On the plus side, it is really amazingly drought tolerant. Even if it is half dead from not being watered, it'll come back.

I know you want blooms, but there are of course tons of foliage plants that are good trailers. I planted purple knight acidenthera (spelling?) last year and LOVED IT. It got really huge. And it is both bushy and trailing.

Still gotta go with superbells or millionbells. They are great performers and if you want floriferous, look no further. Red, yellow, or whatever color you want they have.(I sound like a sales person, don't I?)

Sanvitalia or Bidens are good yellows. I'm not sure if one individual plant would give you a 2' spread, though.

What about the trailing nasturtiums. I used the mounding ones and the trailing ones, one year and they looked great. Took the heat too. C

Oooh, lots of good ideas.

3 seed catalogues in hand, and one on the way =:)

I wish it was time for the greenhouse/garden centres to open, LOL.

This photo is from the summer of 2009 so the garden has matured since then. Although they aren't flowers, these plants (don't know the name of them as a friend was dividing her plants) spill wonderfully over the edges of the raised beds. I think some gardeners consider them invasive but they have been so easy just to trim back and they give the spillover effect I wanted.
Maybe someone else from the forum can identify them.

HTH
Margaret