probably out of your budget, but talk to a concrete/wall/masonry contractor for fun and see what it will cost to make a short wall.

i am of the opinion that you should go big or just do shovel cut edges.

I would dig a shallow ditch around the bed and throw the topsoil up towards the middle back of the bed. Plant the bed and then fine tune lawn edge. Then fill the ditch with mulch and then mulch the rest of the bed as needed.
You've lost some width, but gained a lot in height and depth. I think, all in all, you come out with more root area this way and no sloughing of material from the raised bed to the path or lawn because they're at the same level.
Lawn edgers have to be edged sooner or later, sometimes on both sides. I avoid them when I can.
Mike

What is the depth of the existing soil, that it would limit shrub root growth?

How many inches do you want to raise up?

If pavers on edge take up too much horizontal area, how big is the overall planting space that will not tolerate them?

If you are considering boards, it can be assumed you planting area has a totally straight outline and 90-degree corners? Most board would rot, the plastic/wood hybrid lumber is rated for soil contact.

Any lengthy (8-foot) board material would have to be firmly staked at least every 4 feet to prevent obvious bowing over time.

This post was edited by larry_gene on Sat, Mar 22, 14 at 23:41

Do you have lawn or a sidewalk bordering your flower bed?
Some people use brick. It's not as wide as pavers, and if mortared or concreted in will prevent grass from creeping in.
Rocks are useless, and in my opinion, look ridiculous and require more maintenance.
A picture is worth a thousand words.
Mike

Thanks. I appreciate all the comments.

I decided to use gray paver blocks, about 3 inches thick and 8 x 8.

They are not perfect, but for the 10 feet or so where I need them, they seem to work ok.

Mac