Practically any graphics program can do color -> b/w these days, and you don't have to pay for Photoshop to do it well. Picasa has been mentioned. For quick image stuff, I like Irfanview (free, with lots of plugins that provide additional tools and formats). I also have ACD Canvas - a do-everything illustration program that's probably more competitive with the Adobe Suite + a CADD program than the free stuff (and costs like it; glad I bought a long time ago so I can use upgrade pricing, which is still steep enough that I skip 2-3 versions each time). I've also used Paint.NET (free) and found it decent, though image size is a bit limited (be careful working with RAW or other high-resolution files). I've run across others, especially in the Linux/Windows crossover realm (where the GIMP lives), that are even 64-bit, but without much experience I'd just say, happy hunting! The Corel suite ($$$, like Canvas) is still out there, somewhere. And if you really want Adobe beyond Elements you have to rent it now.

All 3 that I have experience with (Irfanview, Canvas, and Paint.NET) can do basic color->b/w work, including common tweaks like toning (sepia, etc.) and special filters (fractals, oil painting, tracing, etc.). Irfanview and Canvas can also use some Photoshop plugins which allow more extensive tweaking, while Paint.NET has its own "ecosystem" of plugins and extensions.

Irfanview: [www.irfanview.com]
Canvas: [www.acdsee.com]
Paint.NET: [www.getpaint.net]