There are two on-line sites where you can access SDR receivers from around the world:
WebSDR.org has over 30 sites on the home page, some with multiple radios. My 30 meter Softrock receiver, if up, is listed there. The easiest way to navigate the radios is to scroll to the bottom and use the map. You don't need any special client software, just a web browser that has Java enabled. If you want to have your own WebSDR server, be apprised that it must run on Linux. The direct address to my SDR is http://ti2na7u.zapto.org:8080
SDR-Radio.com has a different approach. They supply both a client and server in a single package (go to the Download link) . Both client and server run under Windows. I find their server site a little awkward to navigate, but the client software is a real treat. The waterfall/spectrum is highly configurable, you can set memories, see the grey-line, and a lot more.
If you know of other SDR server software, please drop me a line by e-mail or in the comments below and I'll get it listed. 73! - Casey, TI2/NA7U