I occasionally use signage, although neither my gear nor the vehicles are signwritten - this also helps to keep your contract safe with agencies!.
For my own functions I occasionally use a moving message display. Unlike some DJ's I don't put a rolling 20 minute autobiography on there

, just the basics - name of the Roadshow, My name, Phone Number and invitations for requests. Putting a congratulations message for the person whose function it is, can also be a nice personal touch. (About as close as most people get to that fabled 'Getting your name in lights!').
I also use request slips and find these are very useful, both for customer feedback with regard to music, and for advertising the roadshow. I've had several bookings recently from these. Since I create them myself on a laser printer / photocopier, I am able to customise them for regular resident bookings (With the hotel's details on there for booking the function room etc) this has stood me in good stead with the management of these venues!. I also have a supply of them overprinted with the agency details, so i'm not breaking any contracts, I only work for 2, so its not a big job to convert them.
As Gary mentioned, I give EVERY customer the choice of lighting which they get. Either on my online booking form, or on a written form for telephone bookings. I've done this successfully since around June 2003, and the results, for me, are conclusive. Mainly that the average client does not give a damn about how much lighting you have!. Given the options (at no additional charge) of Nightclub Lighting, Standard Lightshow or Subtle Lightshow - 90% of clients go for either Standard or Subtle - there is no default setting, they have to physically chose, and given the choice they opt NOT to have a lot of lighting.
On the same form, is the option of using a smoke machine. When Given the CHOICE, only 5% of my clients who book, actually REQUEST the use of a fogger. Now I think that says a lot!. I believe in giving my clients say in almost every aspect of their booking from music to lightshow. Okay so Fog makes my lights look pretty, but it wouldn't be at the choice of 95% of my clients, and its not my function its theirs

. Try giving your own clients the choice, chances are you'll find that the £2000 and trailor load of lights that you are lugging around are superfluous.
I think that both Self contained lighting gantries, and T-Bar's have their merits. I have both but prefer the use of a deck / lighting gantry, myself, and I certainly don't find it dominating, but then again I don't set it at a height where it hides me either!

. Certainly the stand is more secure than T-bar's and gives a good platform for mounting a starcloth, which in turn hides the wires.
I do also use T-Bars at some functions , however placing them around a room gives rise to problems such as running very long DMX Link leads around the room. Then having to walk around the perimeter switching off each T-Bar in turn during Buffett breaks for example. I have used these before in larger rooms with 4 T-Bars positioned around the perimeter of the dancefloor with each T-bar holding a Datamoon and a couple of PAR Cans. The ambient effect is excellent and the effect from 1 T-Bar is shown on the piccie below, (no smoke was used, this is just the ambient smoke from guests ciggies showing that you can still be creative and get a good effect without a fogger

)

To make connecting it all up easier, I use a single cable which uses combined multicore mains and DMX Cable, expensive, but meaning that only one cable does the tour around the room, and the lights can be switched/ dimmed / controlled all from behind the DJ Console.
However, I still prefer the Gantry approach and this is the one I use for most functions. The effect is just as good with less setting up. Believe it or not there is only 5 effects on the photo below, but it amply covers a local Police 'space scheme' gig with 800 Under 18's, it can look impressive and easily can be done on a budget of far less than £1000.

For most adult functions, I use the Gantry with more subtle lighting, usually consisting of colour changers and moonflower effects. I still don't recommend the use of Scanners or Barrel Mirror type effects at functions were guests will be seated, since they are very difficult to control and can light spillage can easily annoy people who are seated and trying to talk to the person at the opposite end of the table. The effect (for them) is similar to driving along a road with the sun catching you through the windscreen!,