A project bid should basically contain the information needed for the client to determine whether or not to use your services. It can be delivered in different formats, depending on your or your client's preference (such as paper, a PDF, a single-page site, etc.).
Chris Travers and Canadian Luke had posted answers on a separate question regarding the information that should be included within a bid. The information includes:
A clear description of what is offered, including as appropriate quantity, scope, etc.
A clear description of who is responsible for overruns. This can be further clarified by labelling the document a QUOTATION for fixed bids and an ESTIMATE for estimates of hourly work.
A clear description of payment terms, late fees, etc.
Any other terms of service, either incorporated literally or by reference.
An expiration date, informing the customer how long they have before the rates may need to be rechecked or renegotiated.
Dates the quote can be completed. You need a date for expiration (described in above answer), as well as for when the work can be done, from the time you get the OK. Will this project take 3 working days? Make sure that's on the quote! There is nothing good about saying it takes 3 working days, and 2 1/2 days later, the client wants it done right as soon as he says OK!
How much notice is needed. For larger projects, you may need to give notice for workers or resources to become available. This can be included with the dates, but should be included nonetheless
Depending on the scope or project, you can add a mini-FAQ of questions you believe the client may have, whether it's about the technology or the project itself
Keep in mind that if your bid differs greatly from the contract after you've won the bid (especially in areas of price/scope/dates), then you may end up losing the bid after all (and getting some negative reputation). If there are changes between the bid and the contract, please make sure that the client understands the differences and that they'd accept the differences.