I use "philodendron" - I think it's actually a variegated Scindapsis, very common - in similar situations. The effect is very pleasing, at least to me. There are some very nice Syngonium cultivars available now, and they would also do well.

Reed stem (epidendrum) orchids would look good, miniature elephant ears like Dwarf Jenninsii look good (I use them in combo with neoregelias in beds in the summer)

Madabouteu - i had considered the pothos you mentioned, but it gets out of control and invades the hedges below the balcony fairly easily. The syngonium is an interesting idea, i suspect it may have similar issues since it's a class 1 invasive here... i don't want to cause any problems for the landscape crews. :)

Bihai - interesting ideas! As an orchid lover, i am enamored of the idea to use epidendrums, but don't they need lots of fertilizer, whereas the Neos with the colored foliage aren't supposed to be fertilized at all, are they? I ~really~ like the miniature elephant ears idea, and the type you mentioned are very cute but i've never seen them available locally. What i do have is a nice alocasia 'Polly'. Of course, if i set it outside with our current temps it will probably go dormant... but it would look great in summer. Maybe i'll tuck some cool season annuals into the space for now and plant the alocasia in there in a few months.

Thanks for the ideas so far, they've definitely got me thinking about things i hadn't considered. Any further ideas are welcome. :)

I don't fertilize my epidendrums all that much. They are my most neglected orchids. I may be alone there though (ha ha).
Other things that might set of the colors of certain neos (I guess it would depend on the color scheme of the neos you have) might be smaller broms like Cryptanthus..."Pink STarlight" or "Marble"...or the variegated form of the oyster plant that has the nice pinky/purple thing going on.

I have Dwarf Jenningsii, if you can't find any locally maybe we can trade in Spring. Mine are mostly dormant at the moment.

Thanks for the offer Bihai. Do you think the Polly wouldn't work well once it starts raining?

For anyone who is interested, i planted the blank spot with some vivid orange Kalanchoe blossfeldiana which should be able to stand up to my winter watering regimen (or lack thereof :p ). We shall see! I figure by the time they are done blooming i'll be ready to switch to something more summery in the box.

Part of the Kalanchoe planting involved replacing the cocofiber liner with a new one, those Neos really like those liners, they had all sent roots into the liners, and upon inspection i found the 'Brazilian Pepper' already pupping, weee! :)

I would suggest using some of the various species of Rhipsalis with the Neo's, or perhaps combined with Selaginella. If you are mild enough to use Episica's outdoors, or Streptocarpus, these are also nice smaller shade tolerant plants to combine with bromeliads. Other Kalanchoe species that are trailing could also be nice, or also Black Mondo Grass. I don't know whether various succulents are as easy to grow there with your humidity and summer rains, but Echeverias and Graptopetalum paraguayense also combine beautifully with my bromeliads. For a taller element, why not some Billbergias like B. sanderiana or B. nutans or B. x windii. The Billbergias will all give you winter blooms as well.

As to the Epidendrons, I find for me they stop blooming if they don't get full sun and regular fertilizing. If you do a sort of double potting of the bromeliads with small pots sunk into the larger container, and then use a time release fertilizer for the other plants, it shouldn't be a problem with overfertilizing the broms.