They've all been named now. But I was thinking of Tomas Young (Wasps), Sam Lewis (Worcester), and Dan Thomas (Gloucester). All three had/have a lot of potential, and if it weren't for the strength we have there atm, they could have been potential international players.
I was always impressed with Sam Lewis when he was with the O's, and Dan Thomas was great at U20 level, but never got much of a shot at the Scarlets. Young left the Blues before really getting going, but he looked good, and has put in some good performances for Wasps from what I've heard.
Anyway, enough off topic. I haven't seen the Ospreys v Leinster game yet, so i'll have to keep an eye out for Underhill when I watch it tomorrow. He's got a good mentor in Tipuric that's for sure.