I really like this idea from Seth Godin about how he promoted Squidoo at a trade show:

Here's what we did: we printed 600 t-shirts with a long,hand-written letter on the front, explaining how Squidoo helps eBayers.And we gave the shirt away to anyone willing to wear it. The incentive?Each day, Megan picked someone who was wearing the shirt and gave thatperson $9,000 worth of ads on Squidoo.

Within an hour, you saw orange t-shirts on the show floor. By thesecond day, every single t-shirt was taken and more than 5% of all thepeople there were wearing the shirts.

Total cost: $3,000. (plus the ads).

I really think something similar could work for lawyers or legal vendors at trade shows.  I'd love to give it a try!