I'm fed up with cheap ballpoint pens that produce inconsistent lines. 
What's the best black-ink ballpoint pen I can get for $20 USD or less?

Parker Vector:
http://mall.coimbatore.com/parker/vector/vector.html

You should be able to find a plastic body Vector for about $5, though
they're getting harder to find.  It seems that Parker markets them to
marketing firms for sale with logo imprints.

Best regards,

Omnivorous-GA

You don't want ball point.  You want rollerball.  Uniball is very good.

My favorite is The Parker T-Ball Jotter. See last two paragraphs at 

http://barnyard.syr.edu/~vefatica/bpoint.txt

The Fisher Space pen is the finest I have used or found... it is about
$16 dollors depending on style. You may find it at Staples.

Hope this helps!

My favorite is the Zebra J-Roller. I use a .7 mm medium. It's a very
black ink and copies well. It puts out a lot of ink and you will use
all the ink in the pen before you lose it.

Now the bad news; they've quit making them. I stocked up when I found
out, so I should be good until about the year 2025. They do make some
other gel pens that are very good. You can visit their website at
www.zebrapens.com, then click on gel pens. They're about $1 - $2 each
at office supply stores.

Pilot Precise V5/V7 Rollerball Pens
http://www.officemax.com/max/solutions/product/prodBlock.jsp?prodBlockOID=53403

PV5 Rollerball X-Fine Red - 2pk Item #10014897, Style #25003 2/PK 2.99
PV5 Rollerball X-Fine Black Item #10118446, Style #26010 5/PK $6.99
PV5 Rollerball Assorted Item #10118437, Style #26013 5/PK $6.99
PV7 Rollerball Fine Black Item #10118455, Style #26020 5/PK $6.99
PV7 Rollerball Blue Item #20150293, Style #26021 5/PK $6.99

All that I use.

Hi Omnivorous-GA. I've been looking for a replacement to my 2 Parker
Vectors for sometime. I didn;t find out until today that they are
vecotrs. I could not find anyone at Offie Depot that knew what they
were. Anyway, thanks for the URL. I may now be ablke to replace my
metallic grey and burgendy pens. In both cases, the cover cracked
after many years of use. I found 2 other links that were cheaper but
the color was black only. But I will still include the links.
But the people are right, I can buy them with a logo or plain but in
goups of 50, 100 etc.....
Thanks again!!!
http://www.advantagelink.net/catalog/d/1/index.cfm?p=product&d=679&hid=3947&src=m&f91Y=445&CFID=9265&CFTOKEN=05ABB258-FB48-4609-9BA49266896ACCAA

http://www.shoplet.com//office/db/g2015463.html

Hello,

The best ballpoint pen ever is made by Caran d'ache, excellent
quality, looks good and it's not even expensive! The trick is to find
one outside Switzerland! Hope you find one.

http://www.carandache.ch/products/office/stylos/index.lbl