Notepad++
I usually use the Notepad++, that deals well with big files, allows me to search in all opened files, search on a folder, use a regular expression for the search and even allows the usage of plugins for extra-stuff, like validating XML.
Baretail
For checking the tail of a log that is being written, I like to use Baretail.
Otros Log Viewer
I have already tried Otros Log Viewer, that is good to filter by threads, but I found it difficult to use... maybe it's lack of practice with this tool.
Other text editors for log analysis that I would like to try:
- LogExpert
- Sublime Text