Hi Andrew! Welcome! That's a good mix of hobbies you have. I've strayed away from my professional and recreational programming (although I still seem to be the office go-to guy for Excel VBA - a far cry from OpenCL). My wife is the gardener; I'd probably take more of an interest if you could grow pizza.
Those 290x's would do well on Poem@Home in Boinc. It has Open CL work. The project can be found here: http://boinc.fzk.de/poem/
and our team stats can be found here: http://stats.free-dc.org/stats.php?page ... &team=1247
If you want to venture away from Boinc, as mentioned, they should do well on Folding at Home. http://folding.stanford.edu/
It's a separate client to download, but it's still pretty plug and chug.
These are a couple bio/medical projects good for your GPU. If you're into astronomy or math, there are others. I don't follow them as closely since I really like helping medical research.
Feel free to ask questions, and I'm sure somebody will be along with a helpful answer. There's also lots of good information and fun threads throughout the forum, even if some of them are a little dusty. :-) It's always good to have another brother in Christ on board!