In both cases, Pocket has done books that continue after the series. With
Enterprise, there is just one book so far:
The Good that Men Do by Andy Mangels & Michael A. Martin, with a followup book called
Kobayashi Maru by the same authors due next year.
For
DS9, the post-finale fiction has gone on for, er, a while.

It started in 2001, and has continued full bore since. Here's a list of all the books.
Avatar Book 1 by S.D. Perry
Avatar Book 2 by S.D. Perry
Section 31: Abyss by David Weddle & Jeffrey Lang
Gateways: Demons of Air and Darkness by Keith R.A. DeCandido
"Horn and Ivory" by Keith R.A. DeCandido (in
Gateways: What Lay Beyond)
The above five were collected in 2007 into a single trade paperback entitled
Twist of Faith.
Mission: Gamma
---Book 1:
Twilight by David R. George III
---Book 2:
This Gray Spirit by Heather Jarman
---Book 3:
Cathedral by Michael A. Martin & Andy Mangels
---Book 4:
Lesser Evil by Robert Simpson
The first two books will be collected into a single trade paperback
These Haunted Seas in 2008.
Rising Son by S.D. Perry
The Left Hand of Destiny Book 1 by J.G. Hertzler & Jeffrey Lang
The Left Hand of Destiny Book 2 by J.G. Hertzler & Jeffrey Lang
Unity by S.D. Perry
Worlds of DS9 Book 1
---
Cardassia: The Lotus Flower by Una McCormack
---
Andor: Paradigm by Heather Jarman
Worlds of DS9 Book 2
---
Trill: Unjoined by Andy Mangels & Michael A. Martin
---
Bajor: Fragments & Omens by J. Noah Kym
Worlds of DS9 Book 3
---
Ferenginar: Satisfaction is Not Guaranteed by Keith R.A. DeCandido
---
The Dominion: Olympus Descending by David R. George III
Warpath by David Mack
Fearful Symmetry by Olivia Woods (coming in 2008)
Also recommended are a couple of "previews":
A Stitch in Time by Andrew J. Robinson
The Lives of Dax, ed. by Marco Palmieri
That should keep you busy for a while.
