gaming rig.
i only need: mobo, mem, cpu and gpu.
this is what i got so far, reaching $500. final budget: $600.
 
zipzoomfly prices
Corsair TWIN2X2048-6400C4 2GB Kit DDR2-800 XMS2-6400 Xtreme Performance Memory Retail ***Free Shipping*** $68.90
GIGABYTE Intel P35 + ICH9 Chipset DDR2 1066 ATX GA-P35-DS3L Rev 2.0 Motherboard Retail $88.99  
INTEL Pentium D 2180 800 MHz 775 1MB Desktop Processor Retail ***Free Shipping*** $82.50  
MSI NX8800GT-T2D512E OC Geforce 8800 GT 512MB GDDR3 PCI Express 2.0 Video Card Retail $249.99  
 
Subtotal:    $490.38
 
i will oc, i expect reaching 2.7/3.0 ghz. Now, what will be the best upgrade for an additional $100, a DS3P or DS3R mobo? i don't think it'll make a major improvement above DS3L for this system.
a better ram?
maybe a better cpu?
e4500 2M cache, x11 multi. good room for fsb increase?
e6550 4m cache, but low multi x7.

Doesn't matter what board you get, it will run at the rated cpu & ram speeds, unless you make changes to bios. Still it won't up the FPS by a 100. You need to know your goal. Otherwise, you're shooting in the dark. I think you want to boost gaming performance? If so, then up the GPU to 8800GTS512, which is about $300 after rebate & will last a long while. You can max out every game. Be sure your psu is up to the task. 450W 28A.
 
3.0ghz is a given. Try 3.2ghz. You can go higher with better cooling. Like Infinity, Ninja, Tuniq, Typhoon, TRUE (U120E), etc.
 
None of the Conroe is worth the money, IMO, when they are reaching the 3.6ghz limit on air. The worthy upgrade would be 45nm cpu like Wolfdales.
 
Again, set your goal 1st.

Truthfully for $100 I'd say:
 
1) Upgrade to the GTS.  The GT is loud and runs pretty hot
2) Upgrade your cooling.  (what case are you using?).  You can get an AC 7 Pro to give you some more headroom on the OC

the system is for gaming.
right now i see two options:
 
1) keep the e2180 and get the GTS.
2) keep the GT and get the e4500.
 
option 1 seems to be the right choice.
$80-$90 extra spent on the gts would increase a 10-15% performance in games rather than having the e4500 + GT oc, altough i've read the GT overclocks better than the gts.

 
Not sure where you read that, but the GTS 512 MB overclocks significantly better than the GT (unless you mod the GT with a nice aftermarket cooler, but even then I think the GTS still overclocks better). Its superior dual slot cooler is much better and quieter than the GT's wimpy single slot. Also the extra cache on the E4500 makes only a little difference, and really isn't a worthy upgrade from the E2180. Although I must mention that I've heard the E2160 is a better choice if you're overclocking. Can anyone else confirm this?

I don't think there will be much of a difference between the E2160 or E2180 in respect to OCing.
 
#1 - They are likely the same M0 Stepping.
#2 - They already run so much under the speed they can hit, binning would not make sense.
 
Personally, I would just get the E2160 and save the cash.
(If they were priced the same, I would get the E2180)

oc'ing the e2160, correct me if i'm wrong, but will lowering the multi and set the fsb to 400 to match the ram be the best oc?
400x8=3.2ghz
fsb:ram 1:1

Straight off....stick with the E2160 over the E2180
 
The E2180 has a problem with overclocking and is very power hungry.  The E2160 is much better.
 
1:1 is not necessarily better.  Lower speed on the Ram just means tighter timings and it really doesnt make a difference.  A higher multiplier will create less heat though so I would say leave it at 9.

Agreed with everyone else. GTS512 is the sweet spot. I would've gotten it if it were out at the time of 8800GT release. It's just $50 more.