Domain Flagged For Malware; How To Correct Blacklist

A Wordpress install on one of my domains was compromised a few months ago, and there was a 4-hour window in which the site contained an iframe injection that lead to a malware site.

The problem was corrected, and Google stopped flagging the site as malicious within a few hours after the fix. However, every once in a while I still hear of people having problems accessing the site, all of them I think from within large corporate networks.

Are there a few common list providers that these corporate networks are likely to be subscribing to? Is there a way I can submit the domain for reevaluation? If not, how long would you think a domain would have to be clean in order to repair its reputation on these lists?