It really depends. What is it going to be used for? How much experience do you have with modeling? How much is the photographer willing to pay? How experienced is the photographer and what is the approximate budget of the shoot?
You may want to look at Model Mayhem or One Model Place (websites) and sign up-- they may have some general guidelines for you.
When I use models for my own shoots, I generally do time-for-print where they get paid in prints of the shoot for them to keep for their portfolio or other promotional work-- comp cards, etc. Honestly, I've had more models pay me to shoot them than the other way around.
If you are doing nude work asl for more. If it's clothed or semi clothed, ask for less. If the work will be for sale to the general public, ask for more. On the other hand, if this is fine art or work for the photographer's portfolio, ask for less.
If I was doing something for my portfolio, I'd offer the model $100 to $150 for the shoot, provided he/she has some experience, paid or not. If I was shooting for something where I'd get paid or where I was selling the work to a website, for example, I'd offer a bit more.
To make my long, rambling point in a concise way-- start at $150 and adjust from there. If you want, post in this thread or PM me and let me know as many details of the shoot as you can and I'll be able to give you more of a ballpark. Pay rates for models can be infinitely variable.