I've been using Sphider for the search on Macdrifter and I am extremely happy with the move. For my purposes, I find the search results to be more relevant and the ranking more appropriate than either Google or DuckDuckGo.
I've been tinkering with Sphider Plus this week and I'm planning to switch to this fork. It has more powerful search logic, better indexing rules, word stemming and better overall performance. There's a weird forced-donation model but I honestly don't mind. While Sphider was last updated five years ago, Sphider Plus just received an update a couple of days ago. That's worth paying for.
DataParkSearch looks like one of the most advanced self-hosted search engines I've come across. It supports advanced features like synonyms and popularity ranking. It's quite impressive. I'm not so thrilled with running CGI but I may give it a try.
I'm sold on self-hosted search engines. They require more work but the payoffs are huge.