One thing that many people forget is that the Raspberry Pi is designed to use about 700mA of power. 500mA is provisioned for the SOC chip (the CPU/GPU/RAM and other stuff) and that 200mA is equally divided between the two USB ports (100mA per port).
However, many people dont realize that the USB specification asks that USB ports provide up to 500mA of power. While plugging in your USB WiFi Dongle and take for granted that their desktop machine can easily supply 500mA (or more) to all the ports on them. The Raspberry Pi was designed to support only 2 low powered USB peripherals like say a Keyboard and Mouse.
If the USB port draws more than 100mA of power then there is a polyfuse to hopefully prevent damage. These polyfuses trip it takes several hours for them to reset and allow current to flow once more. Therefore it is best to get yourself a powered USB Hub.
When looking through the list I went and got myself a D-Link 7-Port USB 2.0 Hub. Model# DUB-H7. It works good for me and my configuration. Some people were reporting issues with it. My configuration is Debian Squeeze distro with firmware updated to the latest setup. I'm thinking the firmware is the more important aspect. That said here's my review of the hub.
The DUB-H7 has 7 ports. 2 'fast charging' ports which deliver 5V/1.2A. But they can only do this when a computer is not connected. When a computer is connected they become normal ports providing only 5V/500mA. This means that while I plugged it in and to the Raspberry Pi working from it it was only delivering 500mA of power and I was worried about underpowering it. Anyways I plugged a bunch of stuff in and it didnt choke. Including 2 USB Bluetooth Dongles, 2 USB Flash Drives a Bluetooth headset/charger and stuff and it worked like a champ. Therefore this is a very nice buy in addition to giving me 7 more ports to work with it looks pretty nice too. It's in a nice sleek black case rather than the grey/green case many places show for it.
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