Were you thinking of Phormium, New Zealand Flax? I don't think that would be hardy for you. Are you looking purple foliage plants or purple leaved plants with flowers spikes. Some of the taller Lobelias have purple foliage and then there's Penstemons if they're hardy where you are. There are also Cimifugas one autropurpurea has the color of foliage you're looking for, the bonus here is the fragrant flowers. If you have a somewhat shady spot Ligularia dentata has got chocolate maroon leaves with dark purple underneath. It's the one that gets those big yellow daisy-like flowers.

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Phormium leaves are more of a dusky red-rust color than purple, and I agree that they would not be hardy for zone 5.

Personally, I can't think of a single purple leaved plant with iris-like foliage, flowering or otherwise, but I'd certainly be interested if anyone else can!

there are some purple-tones grasses that may answer your spikiness request, but the best colored ones are less than hardy (annuals)

I thought I remembered seeing a purple leafed iris once, ill need to check and get back to you.

Yep, the Phormium, New Zealand Flax is exactly what I'm looking for. And you're right, not hardy in my zone. Figures! :( Maybe I can find something else but that is what I'm looking for. I'll keep searching.

Thanks anyway.

black mondo grass? I think its a zone 6 and maybe too short but its dark and spiky.

Cordyline, Red Sensation would fit the bill exactly, but again, it is not hardy. It is, however, getting to be relatively inexpensive, so you might treat it as an annual.
You could also put it in a pot, use it as a focal point, and then bring it inside for the winter. It really does give the impression of a purple yucca.

There are several dwarf purple barberries: "Bagatelle", "Crimson Pygmy", and "Royal Burgundy" for three, that have a spiky form if you do not shear them. I know they are not technically perennials, but they sure do add alot to a mixed border. Eucomis, Sparkling Burgundy might fit the bill too, though it is technically a bulb.

I agree with using the dark leaf Cordyline as an annual...they grow very rapidly in the ground.

I've been seeing a lot of pictures and ads of new varieties of Cordyline. Lots of very interesting forms.

And because it is so dramatic, one will do, so it can be easily justified as an annual. As a matter of fact, I've just convinced myself to add one to my perennial bed!!!

I sometimes have used the traditional large floor sized one as a container plant on the patio, (Walmarts - $8), but I think one (or two...?) in the beds will be great.

Oh, thank you! The Eucomis, Sparkling Burgundy and Cordyline are both wonderful ideas. I have the barberries in a bed across from the one I'm working with so that could be an option too.

Here's one more suggestion that's a good reliable for zone 5 - Foxglove Beardstongue 'Husker's Red' - Penstemon digitalis.

A puple tinted cultivar of the native species. Short-lived but reliably self-seeds. Good all season interest - foliage, flowers, seedheads for fall and winter.

I will second the vote for Eucomis. Terranova has one called 'Oakhurst' that is a stunning, rich burgundy with purple undertones rather than red. You might have to treat it like a canna in your zone however.

I'm also have some 'Dark Towers' Penstemon from TNN that is purported to keep the burgundy foliage color longer than 'Husker Red'. We recently had a thread on perennials grown for foliage, you might want to search for it.

I also found some very cute burgundy foliaged Thrift last year but the plant stays so small you'd need seven or so to get much effect. Oh- and there are some dark-leaved wild geraniums ('Espresso', 'Midnight Reiter').

I'm not trying to downplay purple foliaged plants but please bear in mind that the less chlorophyll a plant contains the weaker it will be compared to an all green specimen.

Some good advice I've learned along the way - use the colored foliage plants sparingly such as accents or in little pockets of color rather then a large grouping in a border. This way if a few take a nose dive it's not an expensive endeavor to replace them.

What about planting a purple smokebush in your border. It is easy to prune into a shorter shrub which keeps the intense purple foliage large and attractive. You prune at the expense of the "smokey" flowers of course but get the gorgeous leaves in return.

There are also purple foliage wiegelas, ninebark and elder shrubs which could be considered even "spikier" shaped than the smokebush.

Another easy annual to grow is the Purple Millet, with spikey purple leaves and large tubular seed heads in late summer.