I prefer my Galco King Tuk on the bike. Super comfortable for me and the girls say they can feel it, but that it's not uncomfortable for them either. My girlfriend actually patted me down while riding the other day because she couldn't feel it and wondered why I wasn't carrying. (I thought she was just being friendly, but nope... looking for the pistol..) She didn't find it and actually asked me where it was when we stopped... *Insert joke here about being used to a big gun between her legs...
I typically carry a 1911, so not a tiny weapon, but it is still very comfortable, concealable and can be drawn in the saddle. (re-holstering is slightly more tricky... recommend practice on that one though I have a hard time thinking of reasons to draw while riding..) I also have no body fat for padding, so when I say "comfortable" I really mean it. Sometimes I reach back and check it just to make sure it is still there because I can hardly feel it when riding.
A nice paddle holster works well also, but does tend to print a lot. Open carry is legal here in Ohio, so I don't worry too much about showing, but the King Tuk is absolutely invisible and easily accessible. The only downside is that it is extremely uncomfortable when sitting in a seat with a back, so when you get to a restaurant it's less comfortable and it does print noticeably when you are leaning forward to avoid poking yourself in the spine/kidney with checkered wood grips... (looks like you have a tail.. a very excited tail... LOL)