There are grills on ebay. You can find pictures on this forum of several different types of grills. Trenz, Mr.Grill & E&G Classic spring to mind.
I think there are window deflectors on ebay and I bought mine at
www.weathertech.com. The weatherflectors have a flange that mounts in the window channel. RRUMANER posted a thread with pictures of these. The other type mounts with double-stick tape. I think CaliforniaTitan posted pics of these. As far as Nissan Titan specific stuff, there are a few different bed covers available, A.R.E. makes a hard lid (LSII) and is supposed to have a shell out soon (
www.4are.com), Leer has a shell, somebody posted about a Leonard (sp?) shell, Husky Liners makes floor covers (mats that cover the entire floor area), and Westin has chrome & black bull bars. The Nissan stuff can be seen conveniently at
www.courtesyparts.com. Also, somebody posted about plastic (or rubber?) flares for the wheel wells. I think these were called "bushwacker" if I remember correctly. There are also dash kits (wood, carbon fiber & aluminum, I think) that you can find pictures of here if you search. Oh, and there are some Wet Okole (sp?) seat covers that are custom made to fit the Titan. You can find pics of these posted here also.
There are several different "performance" bolt-ons. K&N makes a drop in filter and a cone filter & intake kit. Volant also makes an intake. Banks makes a cat-back exhaust that you can find a ten mile long thread about. JBA makes headers. Daystar & CST make lift kits.
That's about all I can think of at the moment.