I haven't played in a while, but from memory:
Geodude for mid tier.
Availability Mt. Moon, and if you ever want to pick one up, just head to the nearest non-Diglet cave.
Stats High attack and defense, good HP, bad speed and abysmal special. It seriously gets 1HKO'd by Absorb.
Movepool[/c] Gets Rock Throw pretty early and naturally learns Earthquake at level 36. You'll probably have to use a Dig TM, and it's a great candidate for Rock Slide. It also gets Selfdestruct/Explosion, for what it's worth. Great coverage with Rock Slide and Earthquake gives it enough space to learn Strength without too much hassle.
Typing Rock/Ground. Amazing against normal, poison, electric, and fire, but it gives two pretty bad 4x weaknesses. Anyone whose steamrolled Geodudes using Rattata with Water Gun knows what an Achilles heel this is.
Match ups:
Misty: Don't bother. Gets 1HKO'd by everything.
Lt. Surge: Voltorb's SonicBoom might be a problem if you didn't teach it dig, but none of his other Pokemon can touch him.
Erika: Don't bother. Any grass attack makes Geodude go bye-bye. I guess you could use Selfdestruct to take out one of 'em.
Team Rocket: Resists all the Rattata, Ekans, and Zubats TR can throw at you. Zubat's confusion will be annoying, but Graveler's high defense means that it won't be self-inflicting too much damage.
Koga: Graveler resists Poison, and hits KOs anything of Koga's with Earthquake.
Sabrina: Amazing attack would be great if it had the Special to survive an attack. It might live to take out one Pokemon, but will be KO'd before it can beat a second.
Blaine: Lulz. Just watch out for Fire Spin, although it has to miss at some point, and will do next to no damage.
Lorelei: Don't bother. Rock Slide hits everything for super-effective, but Graveler gets out-sped and KO'd by powerful water and ice attacks.
Bruno: Beats both Onix, and can tank a hit from either of the Hitmons or Machamp, but can't 1HKO.
Agatha: Earthquake hits everything super-effectively except for Golbat, which Rock Slide takes care of. You will have to make ample use of the Pokeflute, and confusion hax will be annoying.
Lance: Gyarados beats it easily, but it walls the rest (barring Dragon Rage's 40 HP,) and even hits Dragonite and Aerodactyl with Rock Slide. Aerodactyl can still cause trouble with Supersonic, and Dragonite can use Barrier to increase the number of Rock Slides it can take.
Rival: Beats: Pidgeot, Rhydon (you probably outspeed, so you don't have to worry about Horn Drill), Arcanine, Exeggutor (with Pokeflute. Barrage and Stomp does squat), and Charizard (when Fire Spin misses). Loses to: Alakazam, Gyarados, Venusaur, and Blastoise.
Conclusion: It's slow, but its amazing defense and good attack allow you to power through the mid-game, so long as you keep it away from special attacks. If you can evolve it into Golem, it beats a good portion of the Elite Four, but as Graveler, it can find itself being outclassed by the late-game. A great tank, but its many bad special weaknesses and horrible special means that it is not a very versatile Pokemon.
Overall: Mid tier.