LogViewer is an open-source tool for viewing and searching massive text files.
The program is extremely fast. We tried opening a 282,000-line file on our test PC and it appeared in less than half a second; we tried again with Notepad and it took 23 seconds; Notepad++ took 8.
The file is displayed with line numbers, too, handy if you need to note the location of some data.
LogViewer can search the file using plain text or regular expressions.
There's support for searching using multiple terms, but this is hidden away on the right-click menu and awkward to use.
Search matches are highlighted, and there are simple filters to show only the matched lines, or everything else (the matched lines are hidden).
What you don't get here are any editing tools. LogViewer is just a viewer: the most you can do is export search matches for analysis somewhere else.
LogViewer's searching features are cumbersome, but for speed it's hard to beat. If you regularly need to view huge logs then grab a copy immediately.