Something that's been working well for me for a few months: a computer on my desk at work, but a folding laptop stand next to it with my laptop on top. SSH/X11 on a fast network makes the two interfaces basically interchangeable, but multitasking between one project and another means that I spend about 4 or 5 hours a day standing and I switch between standing and sitting dozens of times over the course of the day. It turns out that "those tests displaying on the other computer are done running, I should look over the results" is a much better motivator for me to switch positions than "a window from one of those nag-myself apps popped up to warn me to take a break and stretch".

Qualitative definition of "working well": twice this spring/summer I'd developed moderate hip/lower back pain which would be most pronounced when sitting in my usual position and which would last for weeks; that hasn't recurred since I stopped sitting in the same position for 10 hours a day.