Tim Barcz talks about options when it comes to implementing search for a custom site . He suggests two answers: Google and custom built. I'd recommend two more; both of which I've used and been very happy with.
From what I've seen, Google is not quite what I'm looking for when I think about integrating search into my site. It's not bad, but it doesn't give me the feel I'm looking for. Admittedly, I haven't played with it. I'm simply going off of what I've seen around the web. I want something wholly integrated into my web application, not just Google with a logo. Ok, I understand there's more than just that, but I have yet to see a Google search inserted into a site; every implementation I've seen has been the other way around. On the other hand, there are ways to do this with a bit more work... but I'm lazy.
The second option is just plain crazy. Sure, if you've got the time, go for it. Who does, tho? Even if you do have the time, who says you'll implement something completely bug-free? Yeah, right. For this, I have one suggestion that gives you search and a host of other capabilities without limiting your ability to create great .NET sites: DotNetNuke (DNN) . DNN is an open source portal framework or content management system, depending on who you ask. It's absolutely wonderful. That's what I use. While I'll probably get some flack on this comment, think about it as SharePoint-light. DNN is a little rough around the edges and I don't think I'd want to claim the vast majority of the code I've seen, but it is a very good foundation with an excellent extensibility story. Since I'm mentioning it, tho, SharePoint would also be an option; however, I'm not convinced it's the best story for anyone looking for a website. It'll do what you need it to do and then some, but it might be overkill. SharePoint is much more polished and provides a host of features DNN couldn't touch, but the developer experience isn't all it's cracked up to be. I'm going to stay hopeful for the next release, tho. But, I digress...