Mostly depends on what you want to do. Kampala's big but not all that exciting. If you rent a car, make sure its a 4 wheel drive and don't drive at night (well driving in the city at night is ok, but you probably shouldn't drive on the highways at night).

Main night spot area is Kabalagala which is busy all night long (I'm not a night club guy, so have not actually been to any of the clubs).

for food, here's a thread from chowhound:

http://www.chowhound.com/topics/338331

for traditional Ugandan food I like St Anthony's

Internet connections are very poor generally. There's an expensive but reasonably reliable cafe at the one modern shopping mall in town: Garden City

If you take the motorcycle taxies (boda bodas) around, they will automatically ask 4 times the normal charge (I'm assuming you are white, but they also can seem to sniff out any non-ugandan no matter what the race). Offer half that and everyone's happy.

I'm not usually overcharged on the Mutatus (shared taxis). The mutatus take a little getting used to as they have set routes but no indication what those routes are, you end up just learning as you go. Definitely visit the taxi park, just for the experience.

Best (fanciest) hotel in town is the new Serena. A nice small hotel is Emin Pasha but it is a little ways out of town. Avoid the Sheraton (it's showing its age), the Grand imperial and the Speke Hotel both seem nice and are in a good central location.

The best food market to visit is the Nakasero Market which runs everyday and is right downtown.

A good place to get ok coffee with a good view is the cafe in the Worker's House building downtown, it's on the 9th floor and has a good view of the city.

By far the best coffee in the city is at "1000 Cups", they roast their own and you can buy beans from specific growing regions in Uganda. They are near the main police station downtown.

Visit the Kasubi Tombs, it is pretty interesting (but much smaller than you would expect, takes an hour or so)

If you can work it out visit the Gorillas in the west mountains. I've never done it so I don't know the logistics, but it is on my must do list.

There's also a chimpanzee sanctuary on one of the islands that would be interesting to visit.

There's great white water rafting on the Nile.

I think the new Mosque is open for tours now, it is the largest Mosque in East Africa, built by our good friend from Libya, Colonel Gadaffi. It's pretty impressive (at least from the outside)! -- oops, just did a little looking around and it looks like it's not open to the public

Kampala's a pretty safe place relative to other African cities, violent crime against foreigners isn't real common. Petty theft is pretty common, my wife has had a necklace snatched while we were walking around downtown, and just recently she had a bag snatched when leaving a travel agent. But all in all, we've walked around all over town at all hours at night without any problem, just keep an eye out for anything suspicious.

A good web site with a decent map is The Eye Magazine website. The eye is a monthly magazine here.

If you are looking for souvenirs, the market at the National Theatre is pretty good. No matter where you go, almost every shop has the exact same merchandise. The big exception is the art shop in the middle of the market that has lots of original paintings. Usually if I decide I want, I'll just walk from shop to shop and ask each their price for the item, I go back to the the lowest and offer half. There's also a good sized crafts market across from 1000 cups coffee shop.

Have fun! Let me know if there's anything more specific I can help with.