After some reverse-engineering, I managed to find the stats from the Android 2.2.3 version of the game:
+-------------+---------+---------------+------+---------+
| Tower | Damage | # Projectiles | APS | DPS |
+-------------+---------+---------------+------+---------+
| Minigun 1 | 10.00 | 1 | 3.13 | 31.25 |
| Minigun 2 | 11.00 | 2 | 2.84 | 62.50 |
| Minigun 3 | 18.00 | 3 | 2.58 | 139.46 |
| Minigun 4 | 30.00 | 3 | 2.35 | 211.31 |
+-------------+---------+---------------+------+---------+
| Laser 1 | 22.00 | 1 | 1.25 | 27.50 |
| Laser 2 | 88.00 | 1 | 1.06 | 93.12 |
| Laser 3 | 352.00 | 1 | 0.92 | 322.94 |
| Laser 4 | 1408.00 | 1 | 0.81 | 1140.08 |
+-------------+---------+---------------+------+---------+
| Rocket 1 | 150.00 | 1 | 0.40 | 60.00 |
| Rocket 2 | 200.00 | 2 | 0.47 | 188.24 |
| Rocket 3 | 290.00 | 2 | 0.55 | 321.11 |
| Rocket 4 | 440.00 | 3 | 0.65 | 859.76 |
+-------------+---------+---------------+------+---------+
| Shockwave 1 | 53.33 | 1 | 1.00 | 53.33 |
| Shockwave 2 | 140.27 | 1 | 1.00 | 140.27 |
| Shockwave 3 | 368.90 | 1 | 1.00 | 368.90 |
| Shockwave 4 | 970.21 | 1 | 1.00 | 970.21 |
+-------------+---------+---------------+------+---------+
- # Projectiles - meaning, the number of projectiles shot per attack.
- Although it doesn't look that way, the higher-level Minigun tower actually shoots multiple times per "attack".
- APS - Attacks Per Second.
- Apparently the Minigun and Laser towers do shoot slower after upgrading (though this is hard to spot on the Minigun because it shoots more projectiles per attack).
- The Shockwave tower works a little differently (it's a true damage-over-time mechanism). It's best to refer solely to its DPS stat and ignore the damage/projectiles/APS stats.
- DPS - Damage Per Second.
Since the Laser and Shockwave towers have the highest damage and can damage multiple creeps at once, they seem to be the best towers to get in the late-game (along with Lightning towers, of course).