This has already happened to me several times, and I find it rather annoying. I'll be downloading some game on steam, and once a few single MBs remain do be downloaded, the download will suddenly hang, perhaps downloading a few bytes here and there.
This issue may be related to heavy load on steam's servers (recent bundles, and holidays, probably caused a load spike), so there may be nothing to do other than wait patiently.
Still, I was downloading the last few MBs of Really Big Sky for three whole days and if there's anything active I can do to work around this issue, that would be great.