Firstly, thank you for your compliments.

As for your quandary, it is indeed a difficult choice. The Power Mac G5 is not that inexpensive, and the best bang for your buck comes from the high-end Dual 2-GHz G5, which is not good if you are on a limited budget.
My first question is: do you need to use Virtual PC? If you do, and if you really need a new computer soon, then I recommend a Dual 1.25-GHz Power Mac G4. It will use Virtual PC, it is reasonably fast, it is reasonably priced, and it is very expandable. (It even uses Mac OS 9.2.2.) The only problem is that it cannot be upgraded to the PowerPC 970 or any of its successors, as it would require fairly major alterations to the motherboard. For the price of altering the motherboard, you might as well get a new Mac when you need to upgrade to a faster processor.
If the Dual 1.25-GHz Power Mac G4 is too expensive, then try getting a 1.25-GHz Power Mac G4 as your next choice, assuming that Virtual PC is one of your needs.
Note that the Power Mac G4 models may still be upgradable to faster processors if faster G4 processors are released by Motorola. Unfortunately, it is unlikely that anything Motorola will produce for the next few years could match even today's 2-GHz PowerPC 970.
If you are dead-set on getting an iMac if you need Virtual PC, then get an iMac.
If you don't need Virtual PC, then I would definitely suggest a G5. Unfortunately, this also depends on your budget.
For the most bang for your buck, I suggest the Dual 2-GHz G5. For the first time in this century, Apple has released a computer that has similar features and performs at least on par with similarly-priced competition ($3549 Dual 2-GHz Power Mac G5 versus a $3223 Dual 2.66-GHz Xeon Dell workstation and a $3910 Dual 1.8-GHz Opteron workstation from BOXX) and has a superior operating system (albeit the operating system is more subjective than anything else).
Unfortunately, $3000 US is not exactly inexpensive. (Of course, this also gives you an indication of the total bang the Dual G5 gives...

)
This leaves the single-processor models. The 1.6-GHz G5 is difficult to recommend because it is somewhat slow (as far as state-of-the-art processors go) and has been crippled with normal PCI slots and slower RAM. The base model of the 1.6-GHz G5 also has pitiful amounts of RAM. The 1.8-GHz G5 is better, but it is still fairly pricey at $2399. The 1.6-GHz G5, with the same amount of RAM, though, costs almost as much. Don't bother with the 1.6-GHz G5.
So in summary, here are my recommendations:
If Virtual PC is critical:
1) Dual 1.25-GHz Power Mac G4 at $1924
2) 1.25-GHz iMac G4 at $1799 + ~$100 extra for more RAM (256 MB is not nearly enough)
If Virtual PC is not critical:
1) Dual 2-GHz Power Mac G5 at $2999
2) 1.8-GHz Power Mac G5 at $2399