Other than those above..... Bokura WA minna kawaisou PS- I think it was recommended already but read grand blue.....its....... Glorious.
This is my weakness. I don't have any recommendation about romance novel cause i feel it boring and so never read it, so i can't help you eventhough i want. Sorry.
Romantic comedy? It's a bit of a hard request, I know of comedy mangas, and of romance mangas... But both together are something I don't know of many. One that comes to mind is "Where Satans Fear to Tread", it is mostly focused on the comedy however, the romantic aspect of it is secondary at best. It's not one of my favorite mangas, but it gave me some good laughs.