The Raspberry Mint Martini is such a refreshing martini - the muddled mint balances nicely with the fruit and gives your mouth a little zing. The sour mix takes the sugar level down nicely and adds a little zip too - so you end up with a zippy zing of a martini!
By the way, another little tip - if you favor Chambord, the French black raspberry liqueur, be aware this is a high quality product and uses no preservatives so it's shelf life is around six months. You can substitute Creme de Cassis for the Chambord, but remember that Creme de Cassis is made from black currants, not raspberries. I have used both DeKuyper's Razzmatazz and Raspberry Di Amore at times - both somewhat less syrupy than Chambord, but also not as rich in raspberry flavor. Bols has a raspberry liqueur too, though I've not tried it as yet.
Updated 7-2018
PLEASE DRINK RESPONSIBLY
For all you rum lovers out there, here's a retro cocktail that is a classic from way back. The Cable Car uses Captain Morgan's spiced rum, cointreau, a little lemon and a dash of cinammon. 
Number Two in my new line of really, really short stories of martini fiction! Take a short break from your everyday life and ponder the wonders of the "cocktale" world. A novel ideal for happy hour from The Martini Diva.
This is the first of my little illustrated martini nano stories. Just a little literary moment of cocktail fantasy for a change of pace! Enjoy, if you like it let me know with a comment.
The Box Car is a classic cocktail that's been around since at least the days of prohibition. I did a little searching for it's history and came up with nothing on-line, but I do know that gin gained it's popularity during prohibition because it was easy and very quick to brew. Of course, the easier and quicker it was made, the harsher the alcohol and this was the impetus for the explosion of mixed drinks or "cocktails" that evolved during this period - they had to disguise the almost grain alcohol level of the booze they had brewed up that morning in the bathtub, lol!