First off, a gig of RAM versus a half gig of RAM is heavily dependant on what you intend to be doing with your computer. The decision between a gig and a half gig is arguably more important than the memory-type decision itself, at least from a cost standpoint.
For example:
I swear by a half gig of RAM. When I "downgraded" from a gig to a half gig, I
noticed no peformance hit to any of my games. Loading times increased slightly. In synthetic game-based benchmarking, a small performance hit was present. Half gig sets of memory are known to overclock further than gig sets, something which I really enjoy.
One of my friends uses his machine mostly for gaming, owns a mid-end video card, and a mid-end processor. For him, a gig of RAM makes all the difference, and makes or breaks decent in-game performance. My friend doesn't overclock, and runs everything at stock.
The two of us have very different systems, and very different memory needs. Most people prefer a gig of memory.
All that said, the memory decision otherwise really rests in the chip type on the memory sticks that you purchase. I would strongly reccomend TCCD/TCC5 memory, for it's all-purpose excellence. It overclocks well, doesn't need high voltages, can run with tight timings, can scale to quite a high frequency, and most importantly, can be had for fairly cheap
.
Check out these two
excellent and fairly inexpensive 512 meg sets of TCCD/TCC5 on newegg:
G.Skill PC4400 LC -
LINK - guaranteed to 275 MHz with 2.5-4-4 timings, $99. Inexpensive, should overclock fairly well. Won't overclock as well as G.Skill's higher grade memory, but is nonetheless some excellent RAM for the price.
G.Skill PC4400 LE -
LINK - guaranteed to 275 Mhz with 2.5-3-3 timings, $132. This would be my personal pick, these sticks are known to scale very, very well. If you only need a half gig of memory, this stuff will not dissapoint. Pricier than the LC, but well worth it if you plan to overclock aggressively. And if you don't plan on overclocking, the 275 MHz 2.5-3-3 guarantee still nets you some awesome memory performance right out of the box.
And some 1024 meg sets of TCCD:
Corsair XMS 3200XL -
LINK - guaranteed to 200 Mhz, with 2-2-2 timings, $190. I haven't read a lot about this memory, but it should do well given that it's TCCD binned for tight timings at a low voltage. Decent price for what you get. And, Corsair manufactures a great stick of RAM.
G.Skill PC4400 LC -
LINK - same as the LC above, but a 1024 meg set. $236.
G.Skill PC4400 LE -
LINK - same as the LE above, but a 1024 meg set. $256 and worth every penny if you plan to overclock.
OCZ PC4800 -
LINK - OCZ's premium TCC5 memory. Guaranteed to run at 300 MHz 2.5-4-4 out of the box. This stuff costs an arm and a leg, but is still worth mentioning. Expensive, for the price I would prefer the G.Skill memory.
The above are not the cheapest memory options in the world, although they are quite reasonable. Generic RAM can be had for less than $100 per gig.
However, if you intend to overclock and want excellent performance from a low-voltage memory IC, the above are all excellent choices. TCCD/TCC5 really is the king of fall-purpose memory, you can't go wrong with a good TCCD/TCC5 memory stick
. For around ~$100, the half gig sets I linked to are superb choices.