Did a ton of reading on this last week because my G router died for a few days... but returned to life. To summarize my findings I would say that there are a few options out there that will for sure provide significantly greater wireless bandwidth and throughput than the current G offerings but I believe many of the reviews I read stated that there isn't much increase in wireless range and in some cases it's worse.
Along with the un-certified N standard is the option to run on the 5Ghz range rather than the "crowded" 2.4Ghz band which is also supposed to assist in increased bandwidth because you are using a channel not widely used by other devices but I don't believe 5Ghz allowed greater range either. The trouble with the devices that support 5Ghz is that they are more expensive than the standard N and you need a 5Ghz supported device on all of your end points which can be very costly.
If you are in a situation where you have G working and just need increased range I would look into possibly doing another DD-WRT device for cheap and run it in AP or wireless bridge mode. Personally I was glad that my G router came back to life because I didn't have to invest in technology that hasn't officially been ratified just yet and for some reason doesn't seem "complete" just yet.
That being said if you feel you need the increased bandwidth offered by N devices I believe the consensus was that the DIR-655 and the Trendnet TEW-633GR both provided great and affordable single band N performance, supposedly the internal parts on these two are very similar, both can be had for less than $100 now.
I found the reviews and wireless charts at the site below very helpful:
SmallNetBuilder