A couple of days of link-hopping turned up six sites worth keeping. They do not share a theme: online radio, a browser-based Windows imitation, an IP lookup service, phone demos, a daily software giveaway, and Adobe photo storage. Each one is specific enough to be useful.
moradio.cn
This is the cleanest online radio site I have seen. It carries many local and internet stations, both Chinese and international, and includes an on-demand section for book reviews and audiobooks. The layout is unusually spare: a player, a program column, and a large background image. The left and right arrow keys change the wallpaper.
windows4all.com
This site puts a Windows-like operating system in the browser. It requires Silverlight. The interesting part is a built-in Virtual PC feature, though it is not a real VPC as far as I can tell; it seems to be a set of links to online operating systems. It also appears possible to install software, but likely only in a special format. The major limitation is that it does not support Chinese at all.
myip.cn
At first glance this is an IP lookup tool, but it bundles much more: IP address lookup, site information, domain registration details, search engine indexing, Alexa rank, Google PR, Sogou PR, backlinks, Baidu keyword index, and other checks. The feature I find most useful is same-IP site lookup. When I checked my host, it showed 20 sites, some of which were only www and non-www versions of the same domain.
shishouji.com
This site collects Flash demos of popular phones so you can try a model's interface online. It is a reasonable way to get a feel for a handset before buying. The simulations are limited and not especially fun to use, but the collection is broad enough to be worth a look.
giveawayoftheday.com
This one offers a different piece of commercial software for free each day. The license duration is not clear; I have seen it said that it lasts one day. The page shows a timer for when the download link expires. It is an English-language site, but the offer is simple: visit, download, and install before time runs out.
photoshop.com
Adobe's photo service gives you 2GB of storage and an AIR desktop app for uploads. Many people already know it, but the reason to mention it here is direct linking. Images stored there can be embedded elsewhere, and images used in three recent posts have loaded without trouble. The workflow is simple: upload through AIR, get the link from the site, and paste it where needed. The only downside is no Chinese support, which is not a big obstacle in practice.
Delicious, Chi.mp, and FriendFeed also came up during the same browsing, but they are either widely known or blocked, so they do not need another write-up.