A few more options that I use pretty much daily:

• -v for reversing the match (display non-matching instead of matching)
• -e to specify multiple patterns, matching any one is sufficient
• -w to match only at word boundaries, easier to type than the equivalent regexp
• -c for displaying the match count rather than the matches

And some that that I use occasionally:

• -NUM, -B NUM, -A NUM also show NUM lines around/before/after match
• -l to display only the filenames with the matches
• -F “fixed” pattern meaning literal match only rather than regexp. Great to avoid having to quote regexp special characters when you don’t need regexp matching
• -P for PCRE style regexps
• -f to read match patterns from a file
• -q quiet, only produce exit status, no output. Useful in shell expressions (scripts, one liners).
• -a force treating the input as text (useful to override the binary detection heuristic. mnemonic: ascii)