Where next really depends on what you like to shoot. If you shoot wildlife or want more reach then the 50-230/55-200/50-140(with TC) or 100-400.
I don't get the impression thats what you are after but I mention if for completeness.
For me there are two-3 lens you should think about next and these fall under two categories.
1) 35mm F1.4 you have all the versatility you could want with the 18-135 18mm is plenty wide enough for most situations you have a macro(ish) lens all you are missing is a low light monster and the 35mm is such a supremely versatile prime that will allow you to do so much and also if you were travelling with a 2 lens kit the 18-135 and 35mm is great little combo, add the 60mm in for a 3 lens kit and there is not much you can't shoot except very long or ultra wide.
2) 10-24mm or 14mm the 18mm of your 18-135mm is very useful (the 18mm on the 18-55 is slightly better but not by a huge factor) I would sell the 18-55mm and get the 10-24 or 14 depending on your budget/space consideration so you have an ultra wide option.
Personally I find the 18-135mm plus 35mm and 10-24mm is my ultimate travel kit I can fit all 3 lens into a Tenba DNA 8 messenger bag, I have ultra wide covered, I have a fast normal prime and I have the 18-135mm as a walkaround lens and for portraits its a great lens in the 70-90mm range, sharp as thats the sweet spot of the zoom and while you don't get background blur from aperture at that zoom you start getting compression blur and so it works well for portraits at a pinch, Its never going to hang with the 56mm or 90mm primes but it does the job if you want to keep lens to a minimum. Swap the 10-24mm for the 14mm and its an even lighter and more portable kit. That is a great option. I only went for the 10-24 for two reasons flexibility and because I shoot video occasionally and I have high hopes for the next generations Fuji video capabilities and the 10-24mm is ironically hands down the best ultra wide for video in the mirrorless world.
Why?
1) Threaded filter, most other ultra wides from other manufacturers don't have a filter ring so ND filters become a pain.
2) Constant aperture zoom.
3) Super flexible focal range 16mm - 35mm essentially and that is great for the video I shoot which is mainly bands in tight spaces. the 35mm for close up details shots compliments this lens very well. If you have not desire for video or for width below 14mm then get the prime.
However conclusion the next lens I would buy would hands down be the 35mm F1.4 it is still the lens I judge all other in the range by. I still prefer the rendering of it to that of the 56mm and even the 90mm its an awesome lens. There is a lot of hype around the 35mm F2 as its weather sealed and slightly better built (focus ring smoother, aperture ring tighter) but no-one looks at a beautiful picture and says wow I bet that was taken with a lens that had a smooth focus ring. Give it a couple of years and the hype has died down and people will realize the F1.4 is the daddy and the F2 is a great lens if you value compactness and weather sealing highly due to the style of shooting you do.
G
Disclaimer - I have shot extensively with all the lens mentioned above except the 14mm/50-140mm/35mm F2 and 100-400mm, the first three I have used in a shop the other is too new for me to have got anywhere near.
