Hmmm...well, here are a few of things I do (single parent of 3 teenagers - one in college, and two pay cuts over the last two years)
Cell Phones - We mostly use Tracfone, At one point my family of 4 had cell phone service for only $22 a month on their family plan, and their phones are inexpensive too. I recently switched to Virgin Mobile's $25/month plan because I needed a bit more than I was getting from Tracfone, but my kids are still on Tracfone.
Home Phone - I bought an Ooma a few years ago and it paid for itself within a few months. It's a box you plug into your internet router, then you plug your phone into the Ooma box. COMPLETELY FREE HOME PHONE!!! I haven't paid a penny for my home phone service in several years. Pretty cool!
Groceries - I've figured out the cheapest place to buy almost everything we need. Here are some highlights: Smart & Final has 5 lbs. of frozen ground turkey for only $6.00; Costco has 2 HUGE loafs of Kirkland whole wheat bread for only $3.99; Eggs (5 dozen), lettuce, milk are really cheap at Costco; Onions, potatoes, bananas, spices, other produce are usually cheapest at Grocery Outlet; Flour is cheapest at Trader Joes. I hardly ever set foot in a regular grocery store any more, but sometimes shop their sales. Also, I never make a special trip for groceries. I shop at each of those stores on the way to or from someplace else (school, work, etc.).
Newspaper - read it online!
Hair - I've colored my own hair for a long time (Wella - recommended to me by a beautician friend) and buy it at Sally Beauty Supply. I cut down to getting my hair cut twice a year at a strip mall salon for $20, but recently started letting my 15-year old cut it (actually, she cuts the back, and I cut the front). I'm amazed, but it turns out pretty good, I can cut it every couple of months, and it's free!
Clothes - Kid's clothes on eBay can be really cheap. By buying "lots" of clothing you can sometimes buy a whole season's wardrobe for only $1.00 - $2.00 a piece. We also shop Goodwill and Salvation Army, but I don't seem to be able to find everything I need there, so then it's off to Kmart or Walmart.
Extra Money - At the age of 12, each of my kids took the course to become a soccer referee, and they each earn enough money each year to buy all of the clothes, video games, etc. they want. That definitely helps MY budget. I also started doing online surveys to earn a little extra money. I earned almost $200 last year on Opinion Outpost that I used toward Christmas presents. I do surveys on e-Rewards to buy magazine subscriptions.
Dollar Tree - This can be an invaluable resource. They have good equivalents to Oxiclean, dandruff shampoo, toothpaste, Febreze, shower cleaner, toilet cleanser, bleach cleansers, sponges, make-up, etc. - all for $1.00. I was there just last night and found a bottle of 32-load laundry detergent. Haven't tried it yet, but hey - it was only $1.00!
Vitamins, supplements drug store stuff - Sometimes you can find amazing deals on the internet. I find that different sellers have different sales at various times for vitamins. But I also find good deals at Costco and Grocery Outlet. Ooh - also, box of 99 bandaids at Grocery Outlet for only $1.00. Deodorants are often also a good deal at Grocery Outlet. Shampoos and lotions - Grocery Outlet or Dollar Tree.
Everything else - For almost everything I buy that's not groceries (light bulbs, household goods, gifts, etc.) I always check eBay and Amazon. It's amazing how cheap used things can be! I don't always find what I want there, but it costs nothing to check.
I'm sure there's more (I've become quite the penny pincher!), but that's what I can think of for now.
Good luck!