Room EQ Wizard is pretty capable, and is as accurate as your audio interface, but what's good for you depends on what you want to analyze and why . . and where. A computer, an outboard interface, and a bunch of cables is often too much haywire for me unless I'm checking out something that's normally connected to a computer (like an interface, for example). If I'm checking out a recorder or an amplifier, I prefer to use my NTI Minirator MR2 and Minilyzer. They take up very little bench space and run off batteries so there are no ground loops or unintended antennas to interfere with a measurement.
And, sometimes, really, I use an HP 200CD generator and 400 AC voltmeter. The 200CD doesn't have nearly as low distortion as the NTI or a decent computer interface, but if I want to check out the headroom on something that advertises input level up to +28 dBu, I need more than modestly priced solid state test equipment.