To quote myself from a thread with a similar question about a green HeNe versus a standard 532nm DPSS:
"One thing you can't get from a diode based green laser or any diode laser for that matter is this:
2011-05-27_11-15-54pm by
ltkernelpanic, on Flickr
The larger tube is a 543.5 green and the smaller is a 632.8 red HeNe. While I also have green and red tubes mounted in heads a big part of what drew me to HeNe lasers is the beauty of a bare tube in operation."
Or in the case of a multiline argon get
2011-08-06_10-09-08pm by
ltkernelpanic, on Flickr
out of a beam that looks like
2011-08-07_09-50-16pm by
ltkernelpanic, on Flickr
But to answer your question like lasergal said I've been interested in lasers since I saw one in either 6th or 7th grade around 19[redacted]. When I finally decided to start building my own lasers almost two years ago I knew I had to eventually get at least one HeNe for the coolness factor alone. That was a green in a head and after that I had to have a bare tube which lead to the smaller red, followed by a bare green (the tubes in the above pic) and finally a red tube in a head.
Be careful with gas lasers because once you buy one you'll want more and eventually you'll do something crazy and buy and buy a multiline argon like I did. :crackup: Seriously if you're serious about lasers as a hobby a multiline argon is an awesome laser. The one I have produces 6 lines consistently and occasionally 7. You can see 4 or so of them in the pic above.
One serious piece of advice though if you're considering buying a gas laser, especially off ebay, ask about it here first. There are some really knowledgeable folks here. You can find some real treasures on there but most are just your average reds, and a lot are just over priced junk.