First determine why the grass won't grow. I assume that it is because the area is low and floods or holds water. If that's the case you want to address that by either giving the water somewhere to go or by turning it into a bog or rain garden.
A picture would help and describe whether you are looking for construction or layout advice.

Logically you work from the problem to the solution. For some reason you have decided that an island bed is the answer although you assume "that they are not a great idea in terms of landscape design" even though it "Would really only be viewed from one side" making most suggestions about island beds redundant. Would you like to start again?

Problem:
Low lying area where the grass does not grow.

Perceived solution:
Put something else there to mak it go away.

An island might not be the right solution, but it is an idea to start with and get feedback.

The first thing you have to watch out for in this particular situation is that your island does not become a real island. If you don't give the water an alternative place to go, you'll only displace it to the perimeter of your planting bed.

The first question is how would you do that. The second question would be that if you do solve that,would you still feel a need for the island bed.

Island beds are not inherently bad. It is that many are drpped in places that make them relate to nothing which makes them look bad. They need to work with the bigger picture. Sometimes you can tweak the bigger picture to work with the island.

A problem... or an opportunity? Lots of space, water near the surface - sounds like the beginnings of a pond. Unless it's just tree roots and shade prohibiting the growth of grass.

Typical things to keep in mind when creating an island bed have to do with viewing from all sides, so in your case some of them won't apply. If you do decide to add a planting to deal with the problem, you'll still need to know why the grass doesn't grow so you don't end up with the same problem with whatever else you plant there. We're assuming it's wet because it's low.

Without seeing it, the first advice I'd give is not to make it a wavy-edged amoeba. Curves should be large and flowing, and easy to mow around. Make it in scale with the surrounding property. Too small and it looks like what it is: an afterthought, not a deliberate statement.

Pictures would help.

I agree w/ laag. Island beds often do not work because they have no relationship to anything around them.

If you can design an island bed that would relate to the backdrop of trees, I'd say go for it. Also, think of how you can design in layers: tree layer, shrub layer, and ground layer. A large island bed w/o layers can look dinky and out of place.

BTW, I have a similar bed in a low-lying area that relates to the woods behind. I've chosen to plant mostly native plants that like it moist, but don't mind dry periods. My island is rather large and contains:

Trees

- Halesia, Styrax, Sweetbay Magnolia

Shrubs

- Aesculus parviflora
- Callicarpa americana
- Calycanthus ÂHartledge WineÂ
- Ilex decidua
- Sinocalycanthus chinensis
- Clethra 'Fernvalley Pink'
- Cercis chinensis (I got these from a local arboretum's plant distribution, and I must say I prefer them to the native redbud. They are a slowly suckering vase-shaped shrub. The flowering is stunning, and I don't get a million seedlings like I do with the native.)

Ground layer

- Thelypteris kunthii
- Lamiastrum galeobdolon
- Iris pseudacorus