On cameras, where can I find good reliable information on different model numbers?

Nikon has many DXX00 models.
Prices are all over the place.
It would seem the higher the model number the better, thus costlier, the camera.
Canon has many TX and TX1 models.

Added (1). OOPS! Canon has many TX and TXi models.

This is a good place to look up information on cameras
http://www.dpreview.com/...f=mainmenu
For a given camera, you can click on it for more. The Specs tab will have a lot of useful data.

Nikon use a numbering system where the fewer numbers used, the more advanced (expensive) with higher numbers within that bracket denoting more advanced models.

4-digit;

Entry level; D3000 replaced by D3100 and then D3200 (I believe there's a D3300 on the way).

Swivel-screen entry-level; D5000, D5100, D5200.

Medium, motorised body; D7000, D7100 (D7200?).

3-digit models are for advanced amateurs, the current D-600 being full-frame.

2-Digit are obsolete, replaced by 4- digit.

1-Digit are professional.

Canon use a similar system;

EOS 1D Professional, full-frame.

5/6D - amateur full-frame, equivalent to Nikon's 3-digit models.

2-digit - advanced amateur, cropped sensor.

3/4 digits (Rebel in North America) entry-level. T-series replaced X-series. Txi - generally denotes a swivel screen, Tx has a fixed one.

Pentax tend to rely on fewer digits (K-5 advanced amateur/ K-30/K-50 medium, K-500 entry-level) and Sony by a higher initial number (9 -full-frame, 7/6 - advanced, 5- entry-level).

Nikon's D prefix and Canon's D-suffix denote that these models are DSLRs (Canon's 35mm EOS- series have no D-suffix, and considering there's both an EOS 1 and an EOS 5, this is something to look out for).