A good question. You need to check with each individual agent for their requirements, and some use your ability to follow their specific requirements as a gauge of your ability to focus on details and other important things, according to some agent blogs.
AgentQuery is a great resource for agent requirements, but it is just a start. Still visit their own websites to be sure nothing has changed (the same with printed lists of agent requirements such as Jeff Herman's, and Publisher's Marketplace too, that depend on agents updating themselves).
You would most likely not find anyone who wants the full manuscript yet, except if it is a memoir. You will find some agents require the full proposal (and why wouldn't you want to send it if they will take it from the start?), some want a "partial" which varies in definition. In making my list of who to query I have seen a table of contents and two chapters; a synopsis and two chapters; a query letter only plus two chapters, a query letter plus the first ten pages, and more partial varieties. Also, some will want a query letter and CV, others will say query letter only (no sample pages allowed), and still others just say "query" without any further specifications.
From other agent blogs and this forum I have learned that if an agent does not specifically tell you to exclude any sample pages, you should send up to the first 5 pages with your query letter, as most will read them if sent.
Be sure you check if they prefer email or snail mail. If you send a query through email, do not include the pages as an attachment, but just paste them into the email after your query. Send it to yourself first if you do this, to check formatting (MS Word is awful at messing up layout, for example).
Hope this helps, and you can also go to the Bewares and Backgrounds section to find the agent index. There are many agent websites listed in those threads too.
