You need all 10 of these for the Fully Loaded achievement, but don't fret, if you've already gotten a few but don't remember where, you can check your completed quests and it will say the area you found the Claptrap in. Keep in mind that as you get close to one you can hear him crying, so if you hear the noise check around that area. Note: I will not be listing where you find the Repair Kits as once you activate the quest your beacon will tell you exactly where they are. Here we go:
1)Sledge's Safe House
Near the room where the ceiling is broken allowing you to walk up towards a boiler room type area. He'll be behind a shelf and you'll be able to hear him as you approach the other side. Just go up, around, then down and you'll get to the other side of the shelf where he is.
2)The Lost Cave
About halfway through the cave you'll see him, really hard to miss him, hes right out in the open
3)New Haven
Northern part of town
4)Tetanus Warren
Near the first bandit encampment you'll come across
5)Crazy Earl's Scrapyard
At the fork in the road right after Earl's shack, head to to the left and hug the left wall.
6)Krom's Canyon
Take the right path (the way to Reaver) and you'll find him about halfway up on an elevated area near a bandit encampment
7)Old Haven
When you enter the town, stay to the right. Hes in a garage in the Junkyard
8)The Trash Coast
Once you enter go straight until you see a bandit camp, the Claptrap is in the back of the encampment
9)The Salt Flats
Outside a hut in the NE corner of the big mining machine area
10)Crimson Fastness
Hug the right wall
Thanks to GameRadar Forums for info.