If possible, how can I exclude
aspx files from search results in SharePoint Foundation 2010 (+ without Search Server Express) ?
Without Search Server Express there may not be a lot you can do. With Search Server Express you could manage this in a scope definition.
You could try this (...not 100% it will do what you want):
Site Settings > Site Administration > Search and offline availability
Set Index ASPX Page Content to Never index any Web Parts on this site.