This is a bit of breif bit of code:

controller:
<pre>

public List<String> partTypes = new List<String>{'Accessories', 'Electronics', 'Fishing', 'Fun and Entertainment', 'Graphics and Decals', 'Pontoon Covers', 'Safety', 'Seating', 'Trailering and Covers'};

 public Map<String, List<Product2>> availablePartOptions{ get; set;}
.
.
.
List<Product2> boatOptions = [SELECT Id, Name, RecordType.Name, Family,
                                                        (SELECT Id, Name, UnitPrice, Pricebook2Id
                                                          FROM PricebookEntries WHERE Pricebook2Id = :pb2Id),
                                                        (SELECT Id, Standard__c, Maximum__c FROM From_Product_Options__r)
                                                        FROM Product2
                                                        WHERE Id IN :ids];

availablePartOptions = new Map<String,List<Product2>>();
for(String partName : partTypes) {
   availablePartOptions.put( partName, new List<Product2>() );
 }

for(Product2 opt: boatOptions() ) {
  if(opt.RecordType.Name == 'Part'){
    availablePartOptions.get(opt.Family).add(opt);
  }
}

</pre>

Visualforce test:

<pre>

<ul>
    <apex:repeat value="{!availablePartOptions}" var="key">
        <li>
              <apex:outputText value="{!key}" /> -
               <apex:outputText value="{!availablePartOptions[key].size}" />
        </li>
    </apex:repeat>
</ul>

</pre>

This all results in:

Incorrect parameter type for subscript. Expected Number, received Text
Error is in expression '{!availablePartOptions[key].size}' in component <apex:outputText> in page boatbuilder

If I omit the offending line I get a ugly but valid list of keys which is the same as my partTypes List

Accessories -
Electronics -
Fishing -
Fun and Entertainment -
Graphics and Decals -
Pontoon Covers -
Safety -
Seating -
Trailering and Covers -

This is the method every doc I have read said to use when dealing with maps in visualforce.
If anyone has any Ideas it would be a tremendous help