When launching a new web site, there are about a zillion things you need to review before it goes live. Here's my broad-brush, check-list. Of course, there are other tasks that may need to be verified and checked-off, depending on the purpose and scope of the site. But this is a good start.
1) Making sure all the links are live and take visitors to the desired location (of course, usability tests are desirable, but not everyone has time or money to execute these).
2) Using contextual anchor text for links, in order to generate higher results in search engine results pages (For example: You should use, "For more long-term weather information, click here." vs. "For more long-term weather information, click here.")
3) Landing pages are concisely written and effectively route visitors to additional pages, purchasing a product/service or whatever action is desired. (Optimization post-launch is desirable and recommended).
4) Photos and graphics are sized properly and look good, regardless of any browser/screen a visitor may use. All copy is proof-read.
5) Forms (for free-trials, white papers, etc.) work for any browser and deposit information to the right internal recipient.
6) Sign ups for membership, newsletters, white papers, etc. work efficiently, and the information is captured appropriately for internal use.
7) Existing members can easily log-in with their passwords and user names, and access information they had in the past.
8) All applications - everything from APIs to widgets, etc. - work as planned.
9) Forums and other user-generated content can be accessed easily by members, and are thoroughly tested for customer experience.
11) The CMS works efficiently and as planned (there's no surprises about what content appears when).
12) Databases integrated into the site capture all the data desired.
13) Google Analytics or other reporting code is appropriately included in the site, so you can track site performance from Day 1.
14) Data feeds are thoroughly tested and display the data as desired, for any browser or size screen.
15) Ads, if served, display appropriately and back-end reporting is in place.
16) Press releases are crawlable (ideally formatted in HTML or something easily crawled by search engines) and contain link-backs to the main site.
17) Basic SEO is in place. (In fact, you may want to refer to this check list, from SearchEngline Land).