TNT have been around for quite a while. TNT made their name when Tony Harnell joined in the late 80s. Their best albums are _Tell No Tales_, _Intuition_, and _Realized Fantansies_. Other people would replace _RF_ with _Knights of the New Thunder_, which is Tony's first TNT release and which he only sang on (the lyrics were already done when he joined).
Tony has a very amazing voice. His earlier work shows him hitting high notes cleanly, which most of his contemporaries could not do (or even dream of doing). To me, Tony's high vocals gave TNT part of its distinctive sound.
The other part of TNT's distinctive sound is Ronnie LeTekro's guitar. Ronnie can play exceptionally fast and his playing is original enough to separate him from the crowd. You will know whne he plays on a song!
Recently, TNT came out with an analogy which mostly has songs from Tony first three albums: _Knights of the New Thunder_, _Tell No Tales_, and _Intuition_. This would be a perfect introduction to TNT. Afterwards, you can get _RF_ and _Trnasistor_ (but avoid _Firefly_).
BTW, TNT are very big in Japan. Here are some links to Japanese TNT pages:
http://www.norcom2000.com/users/shorin/main.htm (has a boat load of TNT mp3s)
http://users.twave.net/yutaka/tnt.html (owned by a Japanese guitarist who worships Ronnie)
Big Dog