I'd love to use a fountain pen, but for a left-hander they are pretty impractical.
You just have to find the right inks and nibs.
I'm also a southpaw, and find the Japanese pens to be perfect. The two Pilot/Namiki pens (a Vanishing Point, carbon fiber blue just like ederek's pen, and a Namiki Falcon) that I have are
wonderful. Both have Namiki medium-size nibs, which on a European or American pen would be a fine-size. These Namiki pens work so well for my hand that I'll likely never buy another brand of fountain pen. My mom, who is a trained calligrapher and a southpaw, was simply in awe when she tried the Falcon out. It's her favourite (round-nib) pen ever and I'll have to get her one so she won't steal mine. I like both of these pens a LOT more than any Mont Blanc or Pelikan or Parker that I've personally used. YMMV, of course.
The salient features for a lefty are relatively low ink flow (to speed drying) and high flexibility (for smoothness, even when writing on a push rather than pull stroke).
The Noodlers Legal Lapis ink works well for me, and the Namiki blue and black inks write even better, although they are less water-resistant. Other Noodlers inks that I've tried don't dry fast enough for this lefty to avoid the dreaded smear.
I also have about a dozen different 0.7 mm mechanical pencils (Pilot, Pentel, Steadtler), all filled with Pilot HB lead. Jetpens.com is a great place to get all of this stuff, though they admittedly don't have the best prices.