Please feel free to recommend any vendors you used here. It could be for printing services, giveaways, or anything else that would be useful for a convention.
sos.com has used Vista Print in several occasions in the US, UK, and Germany to print the iTunes cards, spice soup cards, and rack cards at different cons.
Advantages: 1. They have very competitive prices, promos, and coupons very often. 2. They are worldwide. 3. They have some free items (you could print some free business cards to promote legendoftheseeker.com for example). 4. They have pretty cool templates, and we've used one of their postcard templates to create the spice soup cards for DragonCon.
Catch: 1. you need to order 3 weeks in advance to get the lowest shipping charges. 2. They are not good if you have a last minute job since their quickest turnaround is 3 business days. 3. When you order outside the US, the VAT/taxes and shipping seem quite expensive.
sos.com has used Fedex/Kinko's to print iTunes cards.
Advantages: 1. They're everywhere in the US. 2. You can order items to be printed at a specific location, so someone can pick them up, and you are not charged for shipping expenses. 3. They have a relatively fast turnaround. 4. They have a store inside the Hilton Atlanta which was a life saver during DragonCon. You can upload your print job(s) at home and pick it up a few days later at DragonCon. Pretty cool!!
Catch: 1. They have a very limited presence outside the US. 2. If you want your items shipped, you have to use their Fedex service which isn't cheap.
Advantages: 1. You can upload your design and print it on a variety of items (e.g. t-shirst, buttons, etc.). 2. They ship worldwide, and the shipping costs are very reasonable.
Tattoo Jet, Tattoo Paper 8.5" x 11" (10 sheets): I've never bought this, but it sure would be a lot of fun to create Seeker-themed tattoos. You can just print them at home with a ink-jet printer and cut them in the desired shape.