HP t5325 thin client, RISC OS, and maybe combining the two. Or just running Linux on it. Either way.
However, as Acorn pulled out of the personal computer market in 1998, the community has had trouble obtaining hardware since. Many users still use circa 1997 RiscPCs with 200 or 233 MHz StrongARM CPUs, which just don't cut it today. While there were a few clones made after the fall of Acorn, most notably the Iyonix (with a 600 MHz XScale,) and the A9home (with a 400 MHz Samsung ARM9-based system on chip,) these machines are expensive for what they are, and the Iyonix is no longer in production. It's proven to be difficult to make custom hardware specifically for this market, as the RISC OS community can't afford custom chips designed for RISC OS machines, so they're required to use embedded chips that provide suboptimal performance, and the low volume causes extremely high hardware prices to make up for development and tooling costs.
But, ARM is now pushing their architecture into the netbook and nettop spaces, countering Intel's attempt to move into ARM's traditional smartphone and embedded spaces. This means that there's now PC-class ARM hardware. And, the best part is, someone else is paying for the development, and ARM wants the volume to be huge.
Not only that, but Castle Technology, the company that makes the Iyonix, has released their version of RISC OS under a shared source license, to RISC OS Open. This has allowed developers to take advantage of the new ARM platforms. Right now, there's a port to the Beagle Board, although it's arguably not well suited towards desktop applications, due to its lack of any form of ATA support, and poor 2D graphics capabilities - the OMAP3530 chip that it's based on is essentially a cell phone chip. Also, it's a developer board, so there's no good case for it. But, there's an ARM platform that's low-cost, commercially available, and does offer SATA, good 2D graphics, and a case.