I'm a big fan of the Lamy Safari and Al-Star pens:Best "budget" pen? under $100? I think this got covered on the old board, but...
Safari: http://www.lamyusa.com/fountain_main_safari.php
Al-Star: http://www.lamyusa.com/fountain_main_alstar.php
They're basically the same design, but the Safaris have plastic bodies and the Al-Stars are aluminum. The nibs are interchangeable and easily pull off for replacement. Lamy makes regular nibs from Broad to Extra-Fine, and you can also get stub calligraphy nibs in 1.1, 1.5, and 1.9 mm widths. A Safari fountain pen is about $30, and the Al-Star is $8–$10 more.