Check out some of the Heliopsis varieties. I'm thinking about getting Heliopsis Sunstruck. I've given up on coreopsis because I've found the deadheading to be a pain. Heliopsis not so much.

Gardengal comment's above duplicate what I would say in response to the question.

Re alternate: as said elsewhere, I've liked Helenium for a long time: 'Goldsturm' and No Name Helenium autumnale (last Aug 18) below. That Helenium starts blooming 2 or 3 weeks before the Helenium.

My experience with Helenium agrees with what you read about it. It doesn't do well in gardens that are allowed to dry out. Also, noticeable with tall Heleniums like 'Sonnenwunder' and 'Flammenspiel', I have always found that they get shorter and shorter (over successive years) if they are not broken apart and replanted every couple of years or so. As previously noted, Helenium can be very long blooming here.

How's this? http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderComments.aspx?kempercode=d231

Or this? http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b461

I hesitate to suggest this one because it won't get as tall as Goldsturm, but Gaillardia 'Mesa Yellow' is a blooming machine from mid spring to frost and beyond. I didn't cut mine back this spring and it's been in bloom for almost a month already. Amazingly floriferous. And a much more pleasing yellow, at least to my eyes, than the more strident Goldsturm.

Another choice would be one of the many new yellow Echinaceas. They are in bloom for months in my garden and they would be a suitable size replacement for Goldsturm. And would keep to size for far longer, too.

I am planting it in combination with Salvia Caradonna so in terms of height, it needs to be taller than the salvia. Came across Heliopsis helianthoides 'Loraine Sunshine' and it seems promising.. lots of excellent reviews but a few say aphids can be a problem or the plant didn't perform as expected. The variegation adds a lot of bonus interest!

'splaker', I am surprised that Goldsturm isn't reliably hardy for you. But I second gg's recommendation of "Little Gold Star" ie it has everything you might like about Goldsturm with none of it's drawbacks. It is one of my favorite, no care, reliably flowering perennials.

'echolane' has suggested Gaillardia. It is for sure a bloom machine but it is my experience as an Ontario gardener like yourself that you may have difficulty successfully overwintering it. (Having said that I could easily see using it like an annual).

Oh did I say it wasn't hardy?? It is.. It's just ubiquitous. Wanted to change it up. Also, I got a lot of black spots on my BES Goldsturm last year..

Another nice one... http://www.perennials.com/plants/echinacea-now-cheesier.html

I think I am going to try this... love the bright, fresh lemony color.... Up to 26" and I think this would look great with salvia! Thanks for the input. Will let others know how I make out! http://www.monrovia.com/plant-catalog/plants/5175/sombrero-lemon-yellow-coneflower/

Golden Gain is a threadleaf coreopsis which I have found to be easy and hardy. In my garden it gets to just about 2' (far taller than any of the other Coreopsis that I grow) and blooms for at least 6 weeks without deadheading, though it might bloom longer if deadheaded. It does spread, slowing sending out runners to increase the clump size. In 3 seasons mine has gone from a small pot to about 3'x1'.

My mistake...not sure why I thought that.

(LGoldS does not get rust/black spot but I guess it is too like Goldsturm for you)

Golden Gain looks great Babs.. thanks...

Although I personally don't want herbaceous perennials which are too vigorous (notably in mixed perennial beds), it may be relevant here to note that species are typically more vigorous (often a lot more vigorous) than some of the cultivars derived from them. Also, the cultivars derived from any particular species are not all equally vigorous.

So from the above, I'd add that Heliopsis helianthoides is likely to be far more vigorous than the cultivar 'Loraine Sunshine'. From my experience and observation (other things being equal), 'Summer Sun' and 'Summer Nights' are both more vigorous than 'Loraine Sunshine'. I've had the latter, and seen the latter, I'd say "lingering".

Also Echinacea 'Cleopatra' (yellow) is nowhere near as vigorous (and long-lived) as Echinacea purpurea or say 'Magnus' or 'White Swan'.

Personally, when choosing perennials, I'd put the potential for survival and the ease of maintenance ahead the choice of colour. But I also tend to feel that the more colours you have in mixed perennial beds, the more additional colours tend to fit in. In addition, particular types of perennials (blooming at different times of the growing season) tend to colour coordinate themselves (e.g. the colour range of summer garden phlox or of fall asters).

For me, being particular about colour is likely to be more important to an artist than to a gardener. I just garden for colour, or rather maybe for colours. And as I said, perennials, by season, often seem to colour coordinate themselves.

UPDATE:

I also like its smaller cousin, Little Goldstar

I second and third this thumbs up. There is nothing not to like about this plant?

Here it is today: