I was going to ask this questions as well... I've begun using a Vac 51 (thanks julio!), and it's quite snazzy... But it's very picky about inks. I was pretty amazed to find that the ink that's played well with every pen and paper I've tried, vintage 60s/70s/80s (?) Parker Super Quink B/B Permanent, didn't like the 51. Went on the paper as a light violet line. Nor did a lot of other vintage inks I've tried- flow was poor, and generally very, very dry. Skrip Jet Black was a light gray. Microfilm Black went on an even lighter gray. Pelikan Black, however, goes on pretty wet and smooth, as does Swisher Midnight Black. I was going to ask myself for recommendations.
That said, vintage Skrip BB is snazzy. I just bought some from vintageinks.com (no association, just a happy customer) which sells various inks at good prices. It's a very green BB, an in some pens it looks not unlike Noodlers Legal Lapis - you could to a 5:1 vintage Skrip BB to Legal Lapis for a "safer" Legal Lapis pretty well.
As an aside, I'm going to post a review of the inks I purchased there as soon as I can find the bleating charger for my camera... Water and bleach tests, and all that. Some surprising results! Here's one of them- Carter's Washable Blue held up the best in the water soak category.

Aaron