Antec 180 or P182 if you want a awesome, yet big and heavy case. Love mine. But they are faily large. There are some great cases out there, but it all depends on what you are looking for in terms of size, cooling, noise, weight, etc.
If you want something smaller, the Antec Sonata III is great, get an additional 120mm low dba fan for the front and it cools very well and is quiet, plus it comes with the Antec Earthwatts 500w PSU, got one for my brothers build for only $89 and it is really a nice combo.
For a motherboard, if you want lots of features and great performance, Abit IP35 Pro (I have always had tons of luck with Abit and DFI), can get them for about $135 now, if you do not need as many onboard features like firewire, just a Gigabyte DS3L or my current MSI Neo2-FR rock for under $100, however my MSI is a better overclocker than the Gigabyte I had.
For memory, if you are not going to overclock, most any major brand of DDR-800 will be fine. Just find what is cheap and go with some 4-4-4 timing stuff if you want a slight bump in performance. I personally love Mushkin and Gskill as they have always OC'd best for me, but other brands are good as well. Had good luck with OCZ, PQI, Corsair, Crucial, TwinMos.
Just be aware that raptors can be loud spinning up, just a nice 320GB 16MB cache WD, Seagate, Samsung, etc drive would perform great and be cheaper.
I do not like to skimp on power supplies. Be sure to get a respected name brand and aim for one with 80% efficiency. Corsair, OCZ, PCP&C, Enermax, Thermaltake, Antec, CoolerMaster (Real Power series), etc have great PSU's and can be had for great prices if you look around. I currently run a CoolerMaster RPP 650w and a OCZ 520W, both are excellent and easily power both my builds. Example: Corsair 550VX is $79 at the egg after rebate.
Onboard sound is not bad these days, but if you want something better and something to take a bit of the load off your CPU, Soundblaster X-FI XtremeGamer is only $51 after rebate right now and it is a great gaming soundcard.