For ABS I use a gel super glue (Loctite is my current favorite), it seems to slightly melt the ABS parts together and makes for a great bond. A slurry of old scrap ABS and acetone also works well, though I find that it will evaporate even if left in a closed mason jar over time. The small nozzle applicator and the fact it doesn't seem to evaporate makes super glue the better choice for me.
The gel super glue works "OK" for PLA but I've had parts fail after taking a small tumble. I just started using this acrylic cement for PLA. It cures very fast but seems to slightly melt the PLA in the same way the ABS options do.
For internal seams I like to put a bead of "high performance" hot glue over the seam. It's just a bit flexible and seems to do a good job taking drops.
Lastly I really like (but haven't mastered) friction welding parts together using a Dremel. Matt Griffin at MAKE Magazine did a great write up on the technique here.