This is the post where I give away a few behind the scenes secrets and make my own project useless to most people. Before breathing life into NerdQuery, I used a couple of tools for multi-site searches. In fact, I still use these tricks for sites that are not part of NerdQuery.
Straight Up Google
You can force Google to do a multi-site search with some Google-Fu. Here's an example of searching "multimarkdown" on three different sites:
It works as expected, but not something you would want to write out every time. It's easy enough to create LaunchBar shortcuts that use these kinds of queries.
Here's a LaunchBar Search Template that searches just a few StackExchange sites:
I have a few of these tucked away in LaunchBar, but those will be my little secrets for now.
Google Custom Search
Google also provides a service called Google Custom Search (GCS). This provides a few advantages over vanilla Google. First, result display can be customized. There are several ways to format the result coloring and fonts. Second, it is preconfigured with sites to search. No need to manually assemble a complex search string. Third, it can pre-index sites using their site maps, to give better results.
The custom search is easily configured with a three step wizard. In the end, you get a bit of HTML and JS to add to a page. You can even do a bunch of douchy things like put the search on your web page to make money off of adsense. I guess making money off of other people's work is the way of the web, but it's not for me.
Google CS is a free service if you don't mind ads, or you can pay $100 to get it without ads. It's actually quite nice but I like the control I get with Sphider-Plus, which powers NerdQuery. It's hard to argue with the simplicity of GCS though.
Here's a basic example of a Google Custom Search. Notice how I've created a similar category grouping of sites like on NerdQuery. This is done with custom labels. It's dead simple.
If you're not up for installing your own instance of Sphider, then I recommend the Google Custom Search for doing the same sort of thing.
But it's easy to argue with ads. Seriously, there are a lot of ads. ↩