I exchanged my Canon D30 to 20D at 2005-03-15. The change was done because of following reasons: better autofocus, better ergonomics and better high ISO performance. Below is my little comparison between D30 and 20D based on actual usage not reading other reviews.

20D pros:

• Autofocus is much faster and more accurate.
• Ergonomics are much better, for example focus point selecting joystick is very good.
• Build quality is better, camera feels much better on hand.
• High ISO performance is much better.
• 8Mpix is more than 3Mpix, but at my use when only publishing photos to internet and printing always A4 size, this isn't very big benefit. Naturally slight cropping can be done and still print at A4.
• Better battery life using same BP-511 batteries.

20D cons:

• File size is much larger, before my 1GB MicroDrive was enough for half day travelling in nature but now it's full in couple hours.
• Setting ISO value is much more difficult than in D30 [in D30 you can set the button inside back command dial to activate ISO adjustment, in 20D you have to press one of the buttons in front of the top LCD-screen and I haven't yet learned (= I will not learn never) to find that button without moving my eye from viewfinder]

Photography links (Link to parent category)

Manufacturers

Canon
Pentax
Nikon
Sigma
Canon - brochures

eStores

AC- FOTO (Germany)
TechnikDirekt (Germany)
New York Camera (Germany)

Finnish Stores

Kuva Lenita (Raahe)
MR-kamera, käytetyt laitteet (Helsinki)
Rajala Camera Pro Shop (Tampere, Helsinki)
Kallioniemi / Superkuva (Tampere)

General

Photo.net
Fred Miranda
Luminous Landscape
Naturfotograf
Digicamera.net (in Finnish)
Steves digicameras
Thom Hogan
Dpreview - Canon SLR talk
Dpreview - Canon SLR Lens talk
Rob Galbraith - D30/D60/10D forum
Rob Galbraith
Pekka Saarinen
Belgium digital
Lone Star Digital
Matti Valve lähikuvaustietoa (in Finnish)
Dpreview
Blog from Eskelinen-Haili-Helenius
Juza Nature Photography

Galleries

Landscape

Humans

Nature

Pekka Saarinen

Techniques

The Canon Digital Learning Center
Calculators

Depth of field (DOF) calculators

DOFMaster - Online Depth of Field Calculator

Other calculators

FOV Calculator

Flash

Strobist (blog): Lightning 101

Cambridge in colour - Hyperfocal distance
Cambridge in colour - Depth of field
Cambridge in colour - Diffraction
Cambridge in colour - Night photography

Nature

Metsähallitus
Pirkanmaan virkistysalueyhdistys r.y.
Birgitan polun kartta
Luontotupa - Kuvia Suomesta!

Equipment

Canon EOS D30

DLC photography - D30 tips
DLC photography - Chuck Westfall's tips
Fred Miranda - D30 FAQ
Reviews

Dpreview
Luminous Landscape 1
Luminous Landscape 2
Rob Galbraith 1
Rob Galbraith 2
Steve's digicams
Photo.net
Digital Outback Photo
Imaging Resource

Flash photography with Canon EOS cameras
Canon EOS FAQ

Pentax

Bojidar Dimitrov's K-Mount Equipment Page
PDML - Pentax-Discuss Mailing List

Lenses

Van Walree Photography - Optics (many good articles)
Canon TS-E lenses

Tilt and shift lenses (regarding all TS-E lenses)
TS-E 45/2.8 on the-digital-picrure.com
TS-E 24/3.5 on the-digital-picrure.com
TS-E 90/2.8 on the-digital-picrure.com
Sports with TS-E lenses by Vincent Laforet for the NY Times
Fred Miranda - how to correct CA when shift used
Cambridge in colour - Shift
Cambridge in colour - Tilt

Carl Zeiss lenses

digLloyd Zeiss ZF lenses
Zeiss.com - Carl Zeiss Distagon T* 35mm f/2.0
Zeiss.com - Carl Zeiss Makro-Planar T* 100mm f/2.0
16-9.net - Test of 28mm lenses including CZ 28/2.8
Pebble Place - Carl Zeiss Planar T* 2/100
Pebble Place - Carl Zeiss Macro-Sonnar T* 2.8/100 N
SLR Lens Review - Contax Sonnar T* 2.8/135mm C/Y
SLR Lens Review - Contax Sonnar T* 2.8/85mm C/Y
SLR Lens Review - Contax Planar T* 1.7/50mm C/Y
Pebble Place - Contax Sonnar T* 2.8/135mm C/Y
Some example pictures of Zeiss lenses
pinciuc.com - samples from various lenses

Nikon PC-Nikkor lenses

16-9.net - Test of 35mm shift lenses
mir.com.my - PC-Nikkor 28mm f/3.5
mir.com.my - PC-Nikkor 35mm f/2.8

Adapters

Pebble Place - C/Y adapters

Cambridge in colour - Understanding camera lenses
Photo.net - Lens tutorial

Canon EOS 20D

Dpreview 20D review
Luminous Landscape part 1
Luminous Landscape part 2
Luminous Landscape field test
Photo.net review

Canon EOS 1D Mark III

The-Digital-Picture.com
Imaging Resource
Ken Rockwell
Rob Galbraith
Photography-on-the.net

Theory

Digital Outback photo - "Image Sensor Size and Field of View" (good chart of common sensor sizes)
Digital Outback photo - "Pixel size"
Photo.net Effects of the physical size of digican sensors on performance by Bob Atkins
Focal length compression explained

Nature

Finland

Retkikartta
Luontoon.fi
Kansalaisen Karttapaikka

Coppice forest near Tampere / Lehdot Tampereen lähellä

Pälkäne, Äimälän lehtoalue
Akaa, Alhonlahden rantalehto
Hämeenkyrö, Vastajärvenojanlehto
Hämeenkyrö, Sasin purolehdot
Kangasala, Hepomäki-Kalkunvuori
Pälkäne, Hausalon lehmuslehto
Pälkäne, Sarkasen harjulehto
Tampere, Iso-Kuhmon lehto
Ylöjärvi, Valkeenkiven lehto
Tampere, Myllypuro 1
Tampere, Myllypuro 2
Pirkanmaan lehdot (miljo.fi)
Valkeakoski, Pappilan tervaleppäkorpi
Valkeakoski, Sydänniemen pähkinälehto
Valkeakoski, Mälkiäisen lehto
Valkeakoski, Vainoniemen lehto
Valkeakoski, Tunturivuoren lehto

Cliffs near Tampere / Kalliota Tampereen lähellä

Orivesi, Eräpyhä
Orivesi, Vuorijärvi
Tampere, polku Kintulammilta Pulesjärven suojelualueelle
Nokia, Huuhkajanvuori ja Kaakkurijärvet
Valkeakoski, Jylhänniemi ja Lapinraunio
Urjala, Kormuntinvuori
Nokia, Peltokankaanvuori
Orivesi, Sonsarinvuori-Raiskionvuori
Orivesi, Huppionvuori
Orivesi, HArjunvuori
Tampere, Neevuori
Tampere, Ahvenvuori-Helaavuoru-Syvälahdenvuoret
Tampere, Peräjärvi - Mustalaisvuori

Pirkanmaa

Luonnonsuojelu Valkeakosken alueella
Luonnonsuojelu - Kangasala
Luonnonsuojelu - Tampere
Luonnonsuojelu - Ylöjärvi
Luontokohteita - Nokia
Pälkäneen suojeluohjelma- ja Natura-alueet
Luonnonsuojelualueet - Orivesi
Luonnonsuojelu Lempäälässä
Pirkanmaan Virkistysalueyhdistys

Panoramic photography

Panotools Wiki (also lot of information which is not Panotools specific)
Panoramic heads

Nodal Ninja
Really Right Stuff
Virtual Reality Photography
360rage - Panorama hardware and heads

Cambridge in colour - Digital panoramas: part 1
Cambridge in colour - Digital panoramas: part 2
Cambridge in colour - Digital panoramas: Projections
Panoguide: the guide to panoramas and panoramic photography
Software

CubicConverter (QTVR)
PTgui
AutoPano Pro
Panoramafactory
PTmac
Hugin

Panomundo QVTR howto

Infrared

Ever wondered about IR photography (Infra Red)