When getting 18s, the ideal tire size to go with is 215/45/18. It's rare but it's the closest to stock tire size when going with 18s. In fact, the shop where I purchased mine informed me that there were only 3 tire manufactureres that make them: BF Goodrich (which is what I have), Toyo, and Pirelli.
civicsir07, I'm running 18s w a 235/40. I have goodyear eagle F1s, which are a great tire, but pretty pricey. This size is almost identical to stock o.d.(one tenth of an inch difference) Personally I chose 18s for ride qualty purpose as I have virtually no change from stock, but 19s look better if thats what you're going for.
consider the Euro-R gets 215/45/17 ... i think it's good to go with 225/40/18 and
235/35/19 ~ 245 is too wide.... remeber we got little tq to run these big ass rims+ tires ~ but 225/45/18 is not bad if u perfer nicer looks than performacne ~