AccountCaseComments.page

<apex:page standardController="Account" extensions="AccountCaseCommentsExtension" showHeader="true" sidebar="true">
  <apex:pageBlock>
    <apex:pageBlockSection>
      <apex:pageBlockTable value="{!account.Cases}" var="c">
        <apex:column value="{!c.CaseNumber}" />
        <apex:column value="{!c.Subject}" />
        <apex:column value="{!caseToCaseComment[c.Id].CommentBody}" />
      </apex:pageBlockTable>
    </apex:pageBlockSection>
  </apex:pageBlock>
</apex:page>

AccountCaseCommentsExtension.cls

public with sharing class AccountCaseCommentsExtension {
    public Map<Id, CaseComment> caseToCaseComment {get; set;}

    public AccountCaseCommentsExtension(ApexPages.StandardController sc) {
        Account act = (Account)sc.getRecord();

        caseToCaseComment = new Map<Id, CaseComment>();
        for (CaseComment cc : [SELECT Id, ParentId, CommentBody, CreatedDate 
                               FROM CaseComment 
                               WHERE ParentId IN (SELECT Id FROM Case WHERE AccountId = '001j000000BwRBl') 
                               ORDER BY ParentId ASC, CreatedDate DESC]) {
            if (!caseToCaseComment.containsKey(cc.ParentId)) {
                caseToCaseComment.put(cc.ParentId, cc);
            }
        }
    }
}