Ticket 19: Different Bar Blues

Because the majority of blues have a standard 12 bar structure it hard not to become entirely predictable when writing one. Adding or subtracting bars is a great way to freshen things up just as your listeners are being lulled into a false sense of security.

Bad Boy
Christmas Time (Is Here Again)
Come Together
Day Tripper
I Me Mine
I Saw Her Standing There
I Want You (She's So Heavy)
I'm Down
One After 909
Revolution
The Ballad Of John And Yoko
Yer Blues

also

Almost (Blues Brothers)
Black Country Woman (Led Zeppelin)
Bodhissatva (Steely Dan)
I Want To Break Free (Queen)
I'm Your Hoochie Coochie Man (Muddy Waters)
Jesus Just Left Chicago (ZZ Top)
Kiss (Prince)
Mission Impossible Theme (Lalo Schifrin)
Oh, Pretty Woman (Albert King)
Pony Blues (Charlie Patton)
Pretzel Logic (Steely Dan)
Riverboat Song (Ocean Colour Scene)
Rock And Roll Music (Chuck Berry)
Subterranean Homesick Blues (Bob Dylan)
The Forecast (Calls For Pain) (Robert Cray)
Trigger Happy (Weird Al Yankovic)
Victim Of Changes (Judas Priest)
Voodoo Chile (Slight Return) (Jimi Hendrix)
Watermelon Man (Herbie Hancock)
Neck Tie (Michelle Shocked)

and

Eight-bar blues like Sitting on Top of the World, Key to the Highway and Heartbreak Hotel

Many old country blues and folk songs, especially by solo guitarists like John Lee Hooker and Robert Johnson have seemingly random numbers of bars.

See also

Ticket 33: Subvert a 12 bar blues song by changing the chord sequence
Ticket 34: Disguise a 12 bar blues song by avoiding the AAB lyric structure
Ticket 35: Use 12 bar long sections in non 12 bar blues songs

See the full list of songwriting tips here - Tickets To Write

Further Reading

The 12 Bar, 13 Bar, 14 Bar Blues
The 12 Bar Blues In Beatles Music Part 2

Thanks to Nancy Rost, T.C. Elliott, Aaron Krerowicz