General

Mine would be:

US3TH3FORC3 *if it'll fit lol*

I already have personalised plates on my car, which are of my nickname.
But if I could, i'd like SUX2BU, but according to my local motoring authority, that plate is unavailable.

I already got one, but always thinking of more, although I need more cars for them. xD

I think mine would have to be B4K3R... and I would also need a Lamborghini to go with it

I used to work for the DVLA (UK equivalent to the DMV) and dealt with Cherished Transfers (moving plates from one car to another, or keeping ownership thereof).
The money these things go for is unbelievable! Even then (1999), a simple one would cost £250, and for something like S1MON or D4DDY - or even a pre-1963 special plate like 1FER (which is assigned to a Ferrari not too far from me) you could easily be looking at five rather than four figures.
Don't waste your money, folks. Spend it on food

on my R34 GTR ive got 3vom

As I mentioned a while ago, I have custom plates (6 letters, no numbers). They cost me $310 back in 2003. Now that my rear plate is cracking and I want a colour change (due to getting a different coloured vehicle), the replacements are going to cost me $655. Definitely better spent on food there, thus I have not replaced them.

I heard of one years ago that went:

I8N8N8

but yes, save the money for more food.