I'll second (or third?) recommendations for Noilly Prat vermouths. I will try others from time-to-time but generally keep bottles of Noilly around as a staple. In addition, I like that it can be picked up in 375ml bottles since I can't go often through a 750ml bottle in the time it takes for vermouth - even if vacuum sealed and refrigerated - to start going stale.
For (gin) Martinis, I use orange bitters and Regan's is my current favorite.