Well I usually ride large frames in the 19-20" range but now those measurement systems are becoming obsolete. Those standover heights really say nothing about the frame size. One manufacturers medium can be about the same as another companies extra large. I look for bikes bikes with around 24" to 24.5" top tubes. My Titus Switchblade for example uses the same standover for all sizes so its impossible to categorize it by any of those sizes. Technically it would classify as a small since the standover is based on the smallest size even though its really an X-large with a 24.6" top tube.
When I got my Schwinn 19inch the guys at my LBS said I was sized for a 17inch, and they said the 19 would be to big. It was a tad big when I got it, but I have grown into it perfectly so all is well that ends well!
I've been riding a large the last two bikes that I had, but then I finally came to my senses and realized that a large is too big for me and I got a medium/17" frame. I was able to get away w/ a large on my Sugar though, because of the frame design.
Mine is a Marin 18.5" but after installing a Marzocchi fork it "grew" a little, Marzocchi fork is a little bit higher than the other. BTW I'm 178cm (5'10")Now it the top tube is a little high for me but I'll have to live with it.
I ride a Kona Kahuna deluxe 18" and I am 165cm... seeing as I'm a girl that seems big compared to what you guys are riding bikes ... but it seems fine to me... my old bike was a Giant Rincon hardtail 19" and too big...