To be realistic, developers are always making something that'll come out in 3-6 months at any give point in time, so you have to decide whether to keep waiting for the next big thing, or enjoy what's out now. If you do decide to wait, don't wait to long, or you'll spend all your life waiting since tech companies won't say "eh, comps are fast enough now, we're done making new stuff. Enjoy the current stuff".
That being said, if you can wait a few more months, you'll have a barrage of new componets to choose from to build your next system, whether it'll be high end or budget. April 22nd is when Intel is adding new CPUs and slashing current CPU's prices, some by 30%. I think their quad-core will go from 900 to 600ish. QC will last you many, many years if you want to future-proof.
Also, nVidia is releasing its mid-range and budget DX10 cards in March, IIRC. They'll be between $100-200, and current gfx cards will drop in price as well. The 8900/8950 is due sometime later. Then there's ATI's r600 series which should come out in May, assuming no more delays. These'll be high-end cards said to rival and even surpass the nVidia's 8800 series. ATI's budget card will come later, I think.
I don't follow AMD news, so they may have goodies coming. For high end/low end, don't know. Other people already mentioned that stuff here, I got nothing to add.
If you can wait til May, you'll have more options and stuff will be cheaper. June/July AMD's new stuff comes. Some time later, Intel will release more stuff. Granted, I don't think you want to wait til the near end of 2007 for a new comp. I say wait til at least April 22nd. If you want ATI's gfx cards, you can settle for a cheapo card for a few weeks. If Intels next chips will work with LGA 775 mobos, you can get an e4300 for $120ish in april to ride out the summer into winter, then upgrade then.