Is "Other" option in selectOneMenu list coming from database?

<h:selectOneMenu value="#{myBean.selectedVal}" disabled="#{myBean.selectedVal == "Other"}">
 <f:selectItems value="#{myBean.selectionList}" />
 <a4j:support event="onchange" reRender="myForm" /> //try container here instead of rendering form
</h:selectOneMenu>
<f:subview rendered="#{myBean.selectedVal == "Other"}"> //Check for String "Other" or whatever option name you have
 <h:inputText value="#{myBean.inpValue}"/>
</f:subview>

ok, then I think you will need to add Other option value to your selectOneMenu list explicitly.