Odd situation here, for years I used a Creative SB Audigy soundcard in my desktop to play soundfonts.  This gave me great real time midi capability, decent sounds, and NO latency.
I've now migrated to Sonar X2 on a laptop.  I use LiveSynth Pro for soundfonts, but even at my lowest latency settings (asio), I get latency.  It's fine for playback, but very hard to record midi without timing issues.
 
Does anybody know of a USB version of the Audigy, or some other hardware device that will playback soundfonts in real time?
I see some USB versions, but none of the descriptions are clear on whether or not they still support Soundfonts.
 
Thanks.

Don't know of any hardware players for sound fonts, but Cakewalk does have sfz+ which is available free from the Cakewalk store. It allows you to play and edit sound fonts. I used to use them but there's so much better sounding stuff available these days.

I think your best shot is a decent USB audio interface with ASIO drivers. Then you can use sf-players and other MIDI stuff with acceptable latency. As you may know, SB-stuff doesn't have a very good reputation around here :o) Buying the audio interface just sound fonts in mind most likely doesn't serve your purpose as a whole, and you do need an audio interface anyway. Your post doesn't mention any interface so I assume you're using the mobo chip, and if so, then most likely ASIO4ALL (which is not ASIOatALL), as the mobo chips usually don't support ASIO.
 
You don't give your laptop specs either, so....
 
Has LiveSynth Pro been updated? This thread gives quite a sad picture of it's usability in multicore systems.
http://forum.cakewalk.com/Livesynth-Pro-is-it-a-nogo-m1885237.aspx
 
According to this you must disable multiprocessing to make LSP work.
 
I mean, there might be something much better for playing soft synths, like sfz+ or Samplelord, both mentioned in the thread.

Thanks gentlemen, I haven't tried sfz+ yet, I'll try it later tonight.  The LS Pro version I'm using is pretty ancient.
 
I am currently using the Steinberg UR28m as my interface to my HP laptop with a Intel G7 CPU (not sure exact model).
 
In the old days, the Audigy was solely for Midi/soundfonts, I used a Delta 66 for the audio.
 
I'm not a fan of Soundfonts per se, it's just that I have a few nice ones I built over the years (favorite pianos, favorite organs, favorite strings, etc).

Not a hardware solution but I would use TX16Wx as it is still being developed and maintained. Of course it is much more than a soundfont player.

I have a steinberg interface too.  I doubt your interface is causing the latency issues.  Laptops have a number of things that can cause latency issues.  I battle them all the time.  Wireless is often a culprit and Nvidia cards on laptops can cause latency issues.  Try this free app to show you exactly what the source is of your problem:  http://www.resplendence.com/latencymon
 
I would be shocked if it is the interface