I usually just fall back on Picasa. What usually needs adjusting is brightness and/or contrast, and it's plenty good enough for those tasks. It's also good at removing things like the "spot" in the sky that results when you've gotten a drop of something on your lens. Not so good at doing color adjustments - for that, you usually need a better tool.
I also like Picassa. Snapfiles has a good selection of freeware and shareware. My own basic favorite is Irfanview although PhotoFiltre7, Gimp and Paint.net are a bit more robust, still easy to use and well thought of. There seems to be a new editor coming out all the time. And don't overlook jAlbum's own image tools in the edit window and those mentioned on the blog (including an auto-correction filter).
I find that DPP (Digital Photo Professional) that is supplied with Canon cameras is easy to use and does a good job with colour adjustment (lighten, darken, contrast, sharpening, saturation etc.) especially for RAW images.
I occasionally use an old version of Fireworks (v3 from last century!) for "airbrushing" and other reprehensible "digital enhancements" .
Cropping is handled quite well with jAlbum's own image tools.
For Apple users, iPhoto, Aperture and Preview (bundled with Macs and includes basic image tools). If you have an iPad (or one of the other tablet devices) there are loads of Apps that have image editing/filters functions, although most (all?) work with jpg, not raw.
I mostly stick with Photoshop, though I have used Bibble in the past, but this is now owned by Corel and called "AfterShot" and I have not tried it.
BUT, it's not a bad subject. A while ago (years?), someone gave a nice writeup on a few editors on the forum, can't find it right now. But in addition to the ones I listed earlier, I've also used FotoMix. I am not a stickler on details and FotoMix doesn't have a huge learning curve so it has fit my needs a few times. For day to day quick stuff, I'm still a fan of Irfanview. Embarrassingly, Haven't made that much use yet of all jAlbum's image tools. The editor is quite good now so I suspect image tools have also gotten very good. Some seem much better suited than others for doing certain things easily: some do drawing arrows well, others quick cropping, and still others for balloon text boxes, etc.