Scopus has a search API, but the documentation and Javascript code they provide is nasty. Here's how to call the API:

http://www.scopus.com/scsearchapi/search.url?devId={YOUR_DEV_ID}&search={YOUR_SEARCH}&format=xml

http://www.scopus.com/scsearchapi/search.url?devId={YOUR_DEV_ID}&search={YOUR_SEARCH}&callback={JS_CALLBACK}

You can add a comma-separated list of fields to return, from the following list:

fields=title,doctype,citedbycount,inwardurl,sourcetitle,issn,vol,issue,page,pubdate,eid,scp,doi,firstAuth,authlist,affiliations,abstract

The result elements you get back (eg 'cited by' counts) are affected by whether the IP address calling the API has a Scopus subscription or not.

To get information for a particular paper, use a search in the form DOI({YOUR_DOI}).

Update: they seem to have disabled XML as a response format, but the JSON response format is still available:

$url = "http://www.scopus.com/scsearchapi/search.url?devId={YOUR_DEV_ID}&search={YOUR_SEARCH}&callback=t";
$data = json_decode(preg_replace('/^t\(/', '', preg_replace('/\)$/', '', file_get_contents($url))));