Cups and pipettes
This is used for measurements that need not be very specific. I use this for trace doses as well as general usage.
Credit Cards or similar
This may sound weird but its a good tool to scrape off things off your tank walls, equipment and hardscape. Get an expired card (or other cards you have no more need for) and just use it to scrape anything you want. They are much more gentle then metallic scrappers and they cost virtually nothing.
I used to use a ruler as it is longer and is supposedly more efficient, but I am not able to handle it really well. I still recommend the credit card.
Pump (Manual)
Some of you would have seen this. I used the hand pump from Daiso which costs $2 and its pretty big and handy. This is good for removing unsightly debris as well as using to clear up thick foliage. For the latter, I used it primarily to "blow" at the moss I used to have in my tank. As moss (or any plant, basically) gets thicker, they have a tendency to trap debris amongst them and this can cause problems. Mainly during WC, I just use the pump to blow across the moss and siphon the trapped debris out.
This list is just what I use. I (and I am sure alot of other people) am very sure that alot of you have some neat tricks and tips. I hope you can add on to this thread, try attaching pictures if you can. It will help.
PS: Sorry for my crappy pics.
-Calvin