Computer excitement for a smart kid?

That's probably about the age when I started learning to program with Hypercard which, like LogoWriter, sadly is no longer an option. From what I've done with it, I think http://hackety-hack.com/ might be a good option. It teaches Ruby programming with a fun little interactive tutorial. A standout blog for kids is http://thekidshouldseethis.com/ which is an awesome, curated collection of kid-friendly videos. There's lots of amazing nature and science content, and well as art and miscellany.

They run their own server and generally keep it reasonably clean. The Aporkalypse is not meant to be kid-friendly, although they tend to keep the cursing to a minimum.

The FTC has a http://www.ftc.gov/bcp/edu/pubs/consumer/tech/tec04.pdf (.pdf) about kids staying safe online.

Google earth is pretty amazing.

I was using the Internet a fair amount when I was 10 (mostly playing HorseLand), but the Internet in 1999 was a whole lot different than it is now. I had an e-mail penpal in Ireland when I was younger than that (through my parents' iquest e-mail) that we found on some website for kids and really enjoyed -- one of my favorite parts was that we would make short .wav files of us saying words that weren't familiar to the other and send them. Your best bet for a well-supervised penpalship at this point might be trying to arrange one through someone you know -- the kid or younger sibling or something of a friend of yours who lives in a different part of the country or another English-speaking country or something. Skyping at some point could be cool. A non-real-name e-mail account might be good if he gets into communicating with people he doesn't know (and you don't either). I recently discovered (thanks to the Blue) http://jakes-bones.blogspot.com/, a weekly blog a ten-year-old Scottish boy keeps about his bone collection. I really enjoyed reading it, and imagine it would be even cooler if I was closer to Jake in age. There are probably also other blogs out there kept by cool kids who are interested in specific things, so he might find one more in line with some of his interests. There are also kids' groups on a lot of interest-related social networking websites like Ravelry and Goodreads (to name two I spend time on); this might be true for other things as well. Throughout my childhood, I dabbled with programming -- mostly Logo, but I also devoted a fair amount of time to HTML and enjoyed creating websites about random things. (And making my HorseLand profile SUPER COOL.) Also, I'd recommend being honest with him about how people lie on the Internet and people can make up personas and stuff, but it's probably not necessary to use the scare tactic-y stories that 60 Minutes specials are made of. Just let him know that there's a lot of advertising, don't give out personal information, and if people are trying to give you things for free, there's probably a catch. (And basic Internet manners: type in a way that's intelligible, say please and thank you, don't use capslock.)

Seconding Minecraft.

http://www.thedreamlandchronicles.com/ is a kid-safe fantasy webcomic. Its style is a little funky because it's actually rendered in 3d for each panel, so the earlier pages are pretty dated looking at this point, but it has a great epic plot with lots of fun characters and the creator actually writes it with their young sons. http://www.zooborns.com/zooborns/ is a never-ending onslaught of adorable baby animals with bonus educational information, if there's someone around to help explain big words and unknown concepts.

Seconding Skype and Lego Digital Designer. you can design whatever you want and order it custom from Lego now. I would have sold my sister for that power when I was 10. Gaming in general can be a fraught issue with kids, especially with the crap you run into on any online multiplayer game. If you decide to let the kid play Minecraft, it might be fun to eventually get them involved with the Metafilter-spawned gaming group http://mefightclub.com. They run their http://aporkalypse.net/ and generally keep it reasonably clean. PG13ish anyway, especially if the mods know a certain user is young. Good kid-friendly webcomics include http://www.sheldoncomics.com/ and http://www.girlgeniusonline.com/ (Although you should check out GG first/ask the parents to see if it passes your/their own filter. It includes mild violence and the occasional victorian undergarment, and the storyline might be a bit complex for a 10-year-old, although I know I would have LOVED the jagers when I was 10.)

+1 for Minecraft, so much cool stuff has been done with redmine circuits and lots of different way to play. Also if they wants to try out programming, http://www.processing.org/ maybe worth a look, some decent http://vormplus.be/blog/article/processing-month-the-overview exist or you could sign up for http://codeyear.com/. If they want to go more hardware oriented, getting a cheap http://www.arduino.cc/ could be fun and make a weather station or something, http://makezine.com/ has more ideas (also http://craftzine.com/). I guessing they are a little young for Cory Doctorow YA titles, I was thinking about http://craphound.com/littlebrother/ in particular but also http://craphound.com/ftw/