So in a year there's my 18th birthday and I'm getting a whole lot of money for it, instead of presents and so on (since I never get anything I use often). I already have a decent graphic card (9800GT) and motherboard supporting every Core 2 Duo and Quad and RAM DDR2. I'm going to upgrade basically everything except for those two parts.
Sorry for prices in PLN - I'll write them in USD at the end.
CPU - Intel Core 2 Duo E7500 2,93 - 599 PLN
RAM - Kingston 2x2GB 800MHz DDR2 - 253 PLN
HDD - 2x Seagate Barracude 500GB (1TB total) - 578 PLN
Pwr Supply - Chieftec 550W - 294 PLN
Total - 1724 PLN, or 548.71 USD or 344.80 GBP.
I already have a very good 22" monitor, gaming mouse and so on. Anything you would suggest I should change or replace? It's going to be June 2010, so prices will go down for sure.
Buying few parts in 2010.
Abedeus
Lord Sojar
By June 2010, you will want to dump into a bigger powersupply, a new GPU (they will be fantastic), probably the cheapest Core2 Quad (from the current release of the best ones) you can find, and maybe a Seagate 7200.12 1TB drive. That will probably run you about 500 USD by June 2010. The 9800GT will probably be going belly up by then, as far as performance is concerned.
Elder III
Personally, I would wait another 10ish months before I started seriously pricing things.. allot can (and will) change in that time, so at this point it would be quite abit of speculation and not much more. If it were me, I'd get one of the newer quad cores for sure and like Rahjah said the 9800 gt will be pretty old hat in a year.... it's getting to that point right now, for new releases anyways. 
Abedeus
Yeah, thanks for the suggestion. I'll make it through the year with my current stuff. I mean, it runs Aion on max with 8x AA... That ain't bad.
Zomgyogi
Don't even bother planning out parts now. So much will change in a year. I started planning out my build 2 months ago and it changed a lot since then.
Josh
I wouldn't bother even planning what parts you want until about a month or 2 before your birthday.. Prices would have dropped dramatically, they'll be a few new series of CPUs, GPUs, etc all out and stuff..