+1 for the Zoom H4n, certainly the cheapest recorder with XLRs. I personally have a Marantz PMD 661 which I also really like.
Also agreed with the stereo/mono comment, most sounds you really only need a mono recording. Saves memory on your recorder too for longer captures. If you want to get stereo recordings, you should look at getting a mid-side rig instead of a traditional stereo configuration. It also requires two mics, but in this case a directional "mid" mic and a figure-8 "side mic". You can convert mid-side recordings to stereo later on with greater control over the width of the stereo field, or use just the mid signal for a good mono recording. The H4n even has a built in mid-side decoder I believe. Also it is less bulky and more robust then an X-Y or ORTF stereo setup, since in mid-side the mics are parallel to each other as opposed spread out at a precise angle.
Also +1 for FreeSound.org, but agreed it does take some searching, though there are definitely some good posts.
Another site I'd like to mention not listed so far is
AudioJungle.net, they have a good selection of royalty free sound effects and also music. It's not free, but very economical and their licenses are pretty clear cut and easy to understand so you know what you're getting. The sounds and music are also moderated, so the quality level is pretty good across the board, as opposed to other audio sites that allow users to post anything and everything. I have bought items there and I also sell a few of my own, it's a nice community and marketplace. AudioJungle also has sibling stock media sites for video, graphics, etc., so it would be useful to find stock video, after effects, projects, etc., for your other video making needs.