In California in the '90s:
AUGHOTI (‘goldfish’)
6E 2OTA (‘sexy Toyota’)
PLARUDE (‘play rude’, on a Prelude)
I had a '48 Willys CJ2A with CJ2 EH, and a '66 MGB with MY 66MGB. The latter was handy when gas was rationed.
I can’t remember ever seeing a vanity plate with numbers between letters.
I think that what’s allowable varies by state; in Illinois, where I live, numbers and letters can’t be intermixed. You can have letters then numbers, numbers then letters, but not number-letter-number or letter-number-letter.
There’s the Virginia plate with CTHULHU.
And if it was photoshopped, it’s still fun.
Best licence plate that never was.
Seen in town, on a silver Porsche:
HI HO AG
[Think: Lone Ranger]
More than 20 years ago (some posted then on a different SDMB thread):
BLACURA (On a black Accura in Richmond, VA)
STILDNCN (On a VW Bug in a hospital parking lot)
MERDALOR (That’s in French)
MUFFDIVR (40 years ago)
8APRIUS (On a Hummer)(current)
B4IM2OLD (On a new Vette)(current)
I question some of those, as I’ve never seen a plate with more than seven characters.
Just thought of another couple from my EAFB days.
MENMYRT: ‘Me & my R/T’, on a Dodge R/T; a takeoff on the ‘Me and my RC’ soft drink commercial.
LKN4TNA: ‘Lookin’ for T&A’. The guy said he told the DMV it meant ‘Lookin’ for Tina’.
3MTA3
Discourse doesn’t like it, the guy driving in front of you will get a laugh.
EATTHE was better
I would have been more impressed with “SUZI”.
I once got passed on I-5 by a replica of the Mach 5 from Speed Racer, which was sporting the tag MACH5GO.
PHAQUE
Or is it?
My all-time favorite!
Regarding MUFFDIVR: Around the same era, I heard about one that said POONTANG. Whoever reviewed that almost certainly did not know what the word meant, nor the one I actually saw that said MENGELE. I reported that one.
Here they will refuse to register supposedly offensive combinations.
I recently saw NO GOD 42. With a nearby Flying Spaghetti Monster sticker.
Best classic rock car plate combo:
Just yesterday I saw a license plate that said “RUT ROW”. 
Even better was the fact that it was on a Connecticut “Caring for Pets“ specialty license plate, which prominently features a drawing of a dog.
If this link works, it is the NC DMV rules for personalized plates which allow a max of 8 digits on passenger cars, if not it’s googlable
I’ve had 8 letters on mine since 1985
And from Wikipedia:
United States license plate designs and serial formats
Vanity_plates) having up to eight characters in a few states.