Yes, it really is no different than a web search engine providing a list of sites in response to a query, but it's always better to get permission anyway. Chances are those manufacturers will be glad to be associated in such away with your site. Who knows, they may even post a link on their site back to you if they list designers on their pages. If you do link to another site without prior permission, be sure to link only to its home page. There have been some disputes about links that bypass a site's home page,(called Deep Linking) because this may effect the linked site's advertising revenues.
Web site publishers have also objected when other sites go beyond linking and use framed content. (another form of deep linking) For example, a site may use three frames on its page, one of which displays text and images from another site. This practice confuses viewers about who owns what content, and it may violate copyright laws. In addition, you should never use a linked site's trademark on your site without permission, even though it would probably be declared a "fair use."
Finally, you should always avoid direct linking – the process of taking another site's graphics or multimedia content by embedding its URL in your own Web page. Direct linking allows a site to use another site's copyrighted material without attribution. This is a clear violation of both Internet ethics and copyright law.
As an added note, be careful of the images you post on your website. Getty Images (the leading owner and licensee of copyrighted images in the world ) has been on a strong campaign to bring claims against web site owners for using images that Getty licenses. See the website extortionletter.info for more details if you are interested. Good Luck with your ste.
Providing a link to another website's homepage is unquestionably lawful even without the permission of the owner of the linked-to website -- so long as the linked-to webpage is not publishing unlawful content. So, providing a link to Broyhill Furniture's homepage is fine (even without its permission) but providing a link to Bob The Pirate's homepage where pirated copies of movies and software can be downloaded is not fine.
There is a distinct possibility that one or more of the manufacturers will refuse to grant permission should you ask. Regardless of who would or should prevail if you offer the link anyway and the manufacturer objects, the dispute process would be extraordinarily disruptive. The only upside to asking is, as Oscar notes, the possibility that the manufacturer will link to your webpage -- the theory being the more links to your website the more business is driven there and the higher your Google rank. So, as always, it comes down to balancing risk: if you ask, they may say no (in which case you should not provide the link) or they may say yes (which gives you nothing you did not already have -- i.e., the right to link, but now they may provide a link to you).
Without a formal affiliate relationship, I doubt that a major furniture manufacturer will provide a link on its website to a retail provider of office furniture (such as your business). So my gut reaction is that asking permission is not worth the risk.
I also think there are probably facts about your relationship with the furniture manufacturers or that business in general that would make my whole analysis worthless. So you should seek the advice of an internet-savvy attorney. Who knows, if done right seeking permission may lead to a close relationship with a manufacturer.
The companies your company prefers to use may well be a trade secret of your company whether you get their permission or not. If anyone in your company figures out you cut and pasted their preferred list of manufacturers you could incur civil liability.