We wrote about a DIY umbrella for two last year at Valentines Day, but now there are a couple of more professional umbrellas for sharing out there: shields that are somehow smaller than a golf umbrella but will still work for more than one person. They're both available through high-end Japanese department store Takashimaya in New York. The portable version (above in red), called the Tri-folding tandem umbrella, looks normal when it's folded, but opens to have two peaks off of just one pole. At $25, it's expensive for a portable, but that red is irresistible for romantic occasions.
The second sharable umbrella is more solid, practical, and likely to last (like a long-term girlfriend). It's black and only has one peak, but it can withstand winds up to 70 mph. At $60, it's an investment that says you're into sharing for the long haul.