How can we manufacture and sell our invention while the patent is still pending?

If you have filed a patent application, you will not lose out on any protection if you manufacture and sell the product.
Your rights will be protected provided, of course, you eventually obtain a patent. As noted, however, be aware of the fact that by manufacturing and selling, you may infringe someone else's patent - consult a patent professional as to checking/vertifying if you are possibly infringing another patent or that you have clearance to manufacture and sell.
Lastly, if you intend to obtain foreign patents, noted that you must file a PCT application or individual patent applications, in those particular countries that you may have an interest in commercializing your invention, within one year of the filing date of your US application.

As long as you filed a patent application comprehensively describing your invention you can move on to manufacture and sell your product. Since your application is filed, disclosing it to the public will not compromise your chances of securing a patent.
Having filed the application, you can mark your product with a "patent pending" label, which may deter competitors from copying your idea. You do not, however, have the right to legally prevent others from infringing until your patent is granted.

In addition to what Limor said, consider doing a prior art search if not already done. This may inform you of whether or not your product may infringe on another. So before you invest a lot of time and money, you can try and do a freedom to operate analysis. For example, say another owns a patent on your product now, you could potentially work around it while your company is in the initial stages.

As you invent improvements, consider filing more applications to create a patent thicket to keep others out of the area (if you can afford it).

Consider a trademark as well. Unlike a patent, they do not have to expire and are cheap in comparison.

Research virtual patent marking enacted with AIA.

Hope this helps,
Mary

If you can pay US$4800, you may apply for quick examination at USPTO without do search by yourself:
http://www.uspto.gov/patent/initiatives/usptos-prioritized-patent-examination-program
This would allow you to receive the issuance or rejection by USPTO roughly within 1 year, that would reveal potential patent that you may infringe. If you do search as suggested by Steven-san, you may file for quick search by submitting the search result to USPTO with US$130: http://www.ipwatchdog.com/2012/01/18/accelerated-examination-is-better-examination/id=21851/