The Tascam DR-44WL was the first recorder I used while learning the craft. It is a great little device to keep in your bag, always ready for use.
The Zoom F3 was perhaps one of the most innovative recorders of recent years, thanks to its compact size and 32-bit float recording capability. It is used by many professionals and offers a simple workflow, very few controls and excellent preamps.
For me, the Sound Devices MixPre-10 II was one of the best investments I could have made. It allowed me to create high-quality surround sound libraries and is renowned for its exceptionally quiet preamps.