There are basically 3 places I go to for 90%+ of my stuff. 2 of them are sponsors here: Bailey's and Sherrill. Out of respect for the sponsors, I am not sure it is appropriate to pass along specific names or links to non-sponsors. The other place I shop advertises on the back of the Buckeye Arborist (the publication of Ohio's chapter of ISA).
Sherrill periodically has safety training stuff in patnership with Vermeer stores. Click on their link in the advertisers' section above and check under the "news and events" tab. Looks like they are done in our area for the year, but I am sure they will have a 2009 schedule as well.
For trade shows close to home: The Ohio Nursery and Landscape Association puts on the CENTS show in Columbus (Jan 26-28, 2009). Definately more targetted towards "landscaping" and less specific towards arborists, but probably worth going to for anybody newer to the field or folks shopping for stuff. More specific to the field of arboriculture and the one I make a higher priority is the Ohio Tree Care Conference put on by Ohio ISA (Feb 22-24, 2009). Smaller "trade show" portion, but much better sessions/classes.