Some programs--notably Web browsers, and especially Firefox 2.0, for which Minimem was designed--"leak" memory as they stay open. Minimem was designed to stop the leaks by removing unneeded memory pages. In theory, it would also help with programs with very large memory footprints.
You can optimize any program Minimem detects, and you can set it to hide programs below a certain RAM footprint. I tried Minimem with a number of my usual applications open, but optimized only the Web browsers. (In theory, I could have used it on the malware scanners that run in the background, but messing with security software is unwise.)The resulting memory bonus was small but perceptible.
Of course, more physical RAM is the best solution for a memory shortage. But if your budget or your case design won't accommodate that, Minimem might boost your system response enough to make your problem applications bearable again.
Note: This program is donationware. It is free to try, but the author accepts and encourages donations towards further development.