Yes, the Denneson "Geometric Soundtracktor" is an excellent device, although rather hard to find. It was distributed by Sumiko, and may still be available from them, although the all-metal version was quite pricey -- around $200, as I recall. I have the plastic version which works equally well, and it originally sold for around $40-50.
There was also a device called the MoFi "GeoDisk" which looked like a heavy turntable platter mat. It also works fairly well, and appears for sale occassionally on Audiogon.
A small company called "Turntable Basics" also makes and sells an alignment and overhang gauge that sells for $20. I bought one, mostly out of curiosity, and found that it works quite well (although not quite as precise as the Dennesen). If anyone is interested, here is the link to the Web site: http://www.turntablebasics.com/
I think that Jerry Raskin's Needle Doctor web site also lists an adjustment device called the DB Gauge. I have no personal experience with it, but it might be worth a look.
Last, there is the Wallytracktor, which is one of several products made by Wally (his last name escapes me). Wally's analog adjustment gizmos are very well designed, although expensive, and for the serious analog-head they are probably a good investment (particularly if you have a couple of friends who are heavily invested in LP playback and are willing to split the cost).
In closing, here is a link to a Web page that has some good discussion of devices for adjusting the tonearm/cartridge combo:
http://www.teresaudio.com/project/digests/align.txt
