MacRumors.com

Hardmac posts what it claims are the product numbers and rough descriptions of the iMac and Mac mini which are expected to be released tomorrow:

The new iMac models and their corresponding references:
- MB417: Entry level model
- MB418: "Mass market" model
- MB419: high-end model
- MB420: ultimate model
The entry level model should come with a 20" display, while the three other models will feature a 24" panel.

For the Mac mini, the references are the following:
- MB463: entry-level model
- MB464 high-end model

They cite a "reliable" source that has told them that both models will become available tomorrow. HardMac.com is the english counterpart to MacBidouille and is generally considered trustworthy.

Earlier today a photo of the Mac mini packaging was leaked and is increasingly looking to be legitimate.

Update: OneMoreThing.nl also "confirms" that the iMac and Mac mini will be released tomorrow and provides the following specs (translated by Sijmen):

Mac mini
- 5x USB
- 1x FireWire 800
- 1x mini DVI
- 1x Display poort
- Nvidia chipset (like the newest MacBook)
- starting at Intel Core 2 Duo 2.0 Ghz
- 1 of 2 GB DDR3 memory (max 4 GB)
- 120 GB hard disk (max 320 GB)

iMac
- one 20" model, three 24" models
- Intel Core 2 Duo (not a quad core): 2.66 Ghz, 2.93 Ghz and 3.06 Ghz
- 1x Display port
- 20" 2 GB DDR3 memory, 24" 4 GB DDR3 memory (max 8 GB)