A good option to start with is the `-help' (or `-?') option.
GHC spews a long message to standard output and then exits.
The `-v' option makes GHC verbose: it reports its version number and shows (on stderr) exactly how it invokes each phase of the compilation system. Moreover, it passes the `-v' flag to most phases; each reports its version number (and possibly some other information).
Please, oh please, use the `-v' option when reporting bugs! Knowing that you ran the right bits in the right order is always the first thing we want to verify.
If you're just interested in the compiler version number, the `--version' option prints out a one-line string containing the requested info.