With all the games out there, there's a bunch of interesting concepts for possible drives, just look at Sword of the stars, freespace, etc.
Options for in- and inter-system travel could include:
Normal ballistic acceleration;
Mass accelerators (like weapons, but with people inside!)
Explosives (Project Orion)
Teleport (possibly a stutter drive that moves ships forward very small amounts)
Hyperspace
Wormholes/Jumppoints
Subspace (like an extra dimension that doesn't only allow long term jumps, but actual movement of sorts)
Sleeperships that travel to a system over 10 years, but leave no emissions until arrival.
Grav-Jumps (Essentially jump points on high gravity points, like BHs)
etc.
I'd love to see a few options in a possible Aurora II FTL, if Steve lives long enough for that.
I'd be nice to see to races clash with radically different technology.