Yamaha TW200 (funky, but I'd need to avoid the M23/M25)
Suzuki RV125 Van Van (as above, sloooooow)
Yamaha MT-07 (could also use at the weekend - bit pricey right now)
Honda NC750 - hmm, bit dull?
Yamaha MT-03 - bit underpowered but prices from two grand
Kawasaki ER6 - meh
Suzuki SV650 - loads of cheap ones, potential
Honda Transalp 650/700 - good ones with ABS available at good value (thanks BSABloke)

What else haven't I seen that would give decent mpg and be capable of motorway speeds (even though the M25 is more of a 50 zone in rush hour)?