I always say choose a silhouette that is timeless, but don't be afraid of a little detail. It's the small details that make the bag. Just be wary of something with big tassels, fringe or large hardware...the more simple the design, the better. Here are just a few of my suggestions for investment worthy black bags...
This one is by Alexander Wang. Love the bowler shape and the small handles and the details are simple, but fantastic.
This Botkier has a little bit more going on than I typically like but I do still think it's classic enough. It's also nice to have the long strap for a cross-body option
The Tallis tote by Tory Burch is a fabulous carryall. It has extremely soft leather and simple styling that keeps it very classic. $525
If I had to choose one of all these, it would have to be the Edye Satchel by Tory Burch $575. I LOVE this bag. It definitely reminds me of a Birkin by Hermes...similar shape and handle. This would be a bag you could love for years.
This would be the best work bag. It's 12" high and 15"long which makes it big enough to carry anything. It's also well priced at $375. By Gryson
I own this Foley + Corinna and it has been a fantastic bag. I got the largest size and I am glad I did. It holds EVERYTHING. It is also incredibly durable $485
The Natasha Bag by Marc by Marc Jacobs is super classic, without many bells and whistles. I like that the strap is long enough to carry over your shoulder and the big gold buckles at the front give it a nice touch. $398
and if you want to REALLY splurge? The Marcie Calfskin small satchel by Chloe is GORG! I adore the fold over flap and the short handles as well as the long strap. This would be perfect back to your favorite jeans or dressed up for work.