Pilot G2 gel pens have really nice dark, flowing ink, and are cheap and readily available. The pens themselves are decent, though I got a Karim Rashid pen* as

Pilot G2 gel pens have really nice dark, flowing ink, and are cheap and readily available. The pens themselves are decent, though I got a Karim Rashid pen* as a gift and was delighted to find the g2 pen refills fit it perfectly. I've heard they fit many other custom pens, too. * It looks like the blocky one in the middle here (http://www.aspshop.net/customs-wholesale/Pens/Karim-Rashid-Imago-Roller-Ball-6380.htm http://www.aspshop.net/customs-wholesale/Pens/Karim-Rashid-I...). That one may or may not work for you - I have big hands.