I work at loads of exhibitions.
You need to consider your target audience. If your industry is predominately male then a nice promo girl/booth bitch will get you a long way. Aesthetic AND quickly able to get up to speed on your proposal/product is important. If you don't want to pay for one then any aesthetically pleasing woman will do, the smarter and more engaging the better!
For a more mixed audience then raffles etc probably won't work, people want immediate reward for visiting your stand. Wiis and similar games consoles are getting pretty popular for enticing people in, it's all about footfall, you want to keep people on the stand not just hand them a leaflet that they will add to the thousands of others in the bin.
Do you have a proper stand or just a shell scheme plot?
If it is just shell then you have a lot of white space to make interesting, posters and or a projector showing video and information about your product is a good way to do this. If you don;t have room for a projector (mock your stand up in the office) the a plasma screen on an attractive stand or cabinet will be just as good.
It is important you work out the layout of your stand before you arrive, don;t just turn up and randomly stick up posters, it looks SO un-professional as do badly lined up projectors, stacks of leaflets on plastic trestle tables and badly produced artwork.
If you have room then some comfortable seating will help, people spend a lot of time on their feet at exhibitions and somewhere to sit down will be welcomed.
Refreshments are good if allowed by the organisers, check into the H&S aspects of hot drinks though, a good coffee for free will get people in.
Oh and most importantly, get off your stand and press the flesh, lots of it. Attend seminars etc and ask questions/actively engage in the event as a whole. don't just sit on the stand looking bored until someone spots you have free pens and humours you for 2 minutes so they can write down someone else's phone number
HTH