A lot of it depends where you're from. Barbara and Colin don't sound particularly unsexy to my ears because they wouldn't have been particularly common names in Dublin when I was growing up. Deirdre, which often gets mentioned on these types of threads seems to have a dreary Coronation Street image in England, whereas here in Ireland it would be considered a traditional celtic name on a par with Siobhan or Niamh or Roisin. Likewise Kevin does not have the same connotations here as it seems to have in the UK
For me, unsexy names would be Philomena, Bernie, Dermot or Vincent because they would be the equivalent of the English Barbaras and Colins.