In Lockwood they give examples of "Smart NICs for Low-Latency Finance" in table 1 from three vendors: Dini Group, AdvancedIO and Accelize.
All three vendors offer good looking cards for PCI Express, SFP+s, and have PPS or GPS timing ports or options for such. Not all the cards in the table are still available as the vendors have moved on and whilst some are still around they also have better and sometimes cheaper ones. Mike Dini's group have introduced a nice Kintex one with PPS timing support for example.
There are plenty of other good vendors out there and here are a few that I'm aware of but I don't necessarily know their product:
- Dini Group
- Enyx - lots of QDR == nice for books
- HiTech Global
- Endace (yes they can transmit too)
- Accolade Technology
- Alpha Data
- TED / Inrevium
- Innovative Integration
- Diligent + Prof Chu's book is an inexpensive and great way to get started
Good dedicated packet capture tech from some of the vendors above (I use Endace and custom in-house cards) and also these guys and gals who aren't really in the transmit space AFAICT:
My company makes stuff like this too with a twist and slice of lemon, but there are many more vendors out there. I'm interested in compiling a bigger list, so please send me firms that you may know of that make PCIe FPGA NIC boards so I may try to learn more about what products are out there.
FPGA's are not always the easiest to use and often you're better off using a fast network card without the FPGA hassle such as those low latency Ethernet NICs available from Mellanox, Solarflare or Myricom. At least kernel bypass has been around for over twenty years now and you should be using it. The real thought is that when you can do 1.3 ~ 2.5 microseconds wire-to-wire with such COTS NIC cards you have to think long and hard about the hassle of an FPGA...
 J. W. Lockwood, A. Gupte, N. Mehta, M. Blott, T. English, and K. Vissers, “A Low-Latency Library in FPGA Hardware for High-Frequency Trading (HFT),” 2012 IEEE 20th Annual Symposium on High-Performance Interconnects, pp. 9–16, Aug. 2012.