you'll get lots of replies telling you to buy nikon / canon etc from the brand fanboys on here (nowt wrong with them of course - hanker after a D3 or 5D myself).
Have got a couple of pentax dslrs - an K10D and a much older ist DS - more than happy with both - especially like the k10d for the money I paid - image quality is good (shoot RAW though), handles nicely and packed with some good features for the price range (when it came out). Have used both in both hobby and also pro (weddings and portraits) and always been pleased with the results
looking at the spec, I am guessing that alot of the k10D is now being used in the K-m or K2000 - with the posh model being the K20D (talking about 10mp sensor etc here) but in a smaller body (probably the size of the ist DS - which with a small lens on is easily pocketable in a coat)
I kind of stuck with pentax as had flm slrs by them, plus the easy access to some nice 2nd hand lenses - the K mount has been around for years) was appealing - although lens prices have gone up due to people realizing what good cameras they are and the quality of the glass (for little money cf to the equivalent canon/nikon quality)
my bits of advice would be:
1) go handle and play - find a dealer who will let you - see how it feels in your hand etc cf to entry level other brands (no good buying a camera that doesnt feel right as it wont be a pleasure to use)
2) if you can take some trial images as well - to see what the quality is like
3) (not sure this still applies) but the kit lens which used to come with the pentaxes (16-55mm) was soft and showed lots of fringing. Budget for some new glass (would recommend an older pentax 50mm 1.4 or 1.8 (makes a cracking portrait lens - and can be found pretty reasonably 2nd hand (NB you will need to shoot manual rather than in p mode with this one as it doesnt have automatic apeture), tamron 18-200mm for a wide range zoom or a sigma 17-70 f.28 for a general lens)
4) learn how to use it properly - a dslr wont (as I ma sure you know) make you a great photog overnight - but a entry level dslr will allow you to learn how to take a great pic
god that was a long ramble! sorry