One of my favorites, even though it's a kid's book, is Dragon's Blood by Jane Yolen. It was a trilogy but I only really liked the first one. Of course the Song of Ice and Fire books (George RR Martin) have great dragons, hopefully they play a bigger part in Winds of Winter. Eragon wasn't bad, though the talking parts got to be a bit much. I haven't found many adult fantasy novels where dragons play a significant role in the plot though, suggestions?