I went through this about six months ago. I had several WRT54GLs. They performed beautifully for years but then all three of them started having major packet loss problems on wireless around the same time. Literally within days or weeks of each other. I feel like there is some sort of time bomb bug in them. It could also have been the Tomato firmware that was loaded on them. I tried to notify the creator of Tomato or find out if others were having the same problems, but never got any response.
In any case, I had quite a bit of trouble finding something that 1) wasn't too expensive, 2) supported Wireless-N dual band, 3) had a 10/100/100p (Gigabit Ethernet) switch, 4) did not have too many reports of problems, especially with wireless packet loss,and 5) was supported by DD-WRT or Tomato firmware.
One thing I learned fast: don't go with the new Cisco/Linksys SOHO "ashtray" devices. They are crap. They are fully enclosed in a plastic ashtray-looking shape, including the antennas. Reports of poor signal strength and overall failures due to overheating are everywhere.
I ended up getting a Buffalo WHR-HP-G300N. It's Wireless-N, but it is only the 2.4 Ghz band (not the dual-band 2.4 Ghz and 5 Ghz that Wireless-N supports). The built-in switch is also 10/100 (Fast Ethernet), not 10/100/1000 (Gigabit Ethernet). Still, it was cheap and Buffalo has a custom build of DD-WRT just for this device. It works great for me. My desktop has a 10/100/1000 network card, but my server only has a 10/100 card and my Internet is "only" 20 Mb, so I have no use for Gigabit Ethernet at this time anyway. I would have liked 5 Ghz wireless support but I purchased 5 Ghz cordless phones a few years ago so they wouldn't interfere with my 2.4 Ghz Wireless-G network, so I would probably have ended up using 2.4 Ghz Wireless-N anyway.
I would definitely go ahead and go with a Wireless-N device. Pretty much all wireless NICs coming out now are Wireless-N. There is no reason to stay back on Wireless-G at this point as Wireless-N is backwards compatible with Wireless-B and Wireless-G devices. Dual-band Wireless-N access points are also backwards compatible with Wireless-A.
Keep this in mind: the 5 Ghz spectrum is much less crowded and has support for more non-overlapping channels in the U.S. than 2.4 Ghz does. This is important because to fully take advantage of Wireless-N, you want to use a 40 Mhz-wide channel instead of the traditional 20 Mhz-wide ones. You can set a Wireless-N access point to use a 40 Mhz channel in the 2.4 Ghz spectrum, but you then most certainly having pretty significant overlap with neighboring channels and therefore more interference. That said, 5 Ghz never really took off in the consumer space so you see a lot of 2.4 Ghz single-band Wireless-N stuff out there, both for access points and for NICs. But if you can do 5 Ghz you should. You'll get better throughput and less packet loss.