Indexer expressions like {{ myproperty[2] }} should work.

[krisnye]

Of course you should also be able to nest an expression inside it like this {{ myproperty[ myotherproperty * 5 ] }}

[arv]

Here is a test

arv@7b4b2be

[rafaelw]

I believe this is now fixed

[kaosat-dev]

I might be missing something, but it seems like this does not work in all cases :
If you have an attribute like this one:
objArray:[{name:"foo"},{name:"bar"}]

In a template , this works
{{objArray.0.name}}

but this does not
{{objArray[0].name}}
(throws error : Invalid expression syntax: objArray[0].name)

I also whipped up a jsbin for clarity:
http://jsbin.com/iFUlEBAp/2/edit?html,output

[rafaelw]

Good catch, @kaosat-dev Fixed here: googlearchive/polymer-expressions@fd80253