In another thread Frogboy mentioned he wanted to know how players beat suicidal. Here are my two cents:

Sure, I can tell you how I beat 8+ AIs on Suicidal: (And no Ctrl-n cheese, play with what you've got)

First - Money. I need to do everything I can to maximize my money so that I always produce at 100%. Always spend the 4 points for +30% economy boost. Go evil to get a +100% economy boost.

Second - Diplomacy. Starting out I research xeno comm, univ trans, diplomacy, trade, interstellar, alliance, republic, adv diplo >> total majesty, and then democracy and federation in that order EVERY game - from there I look and see what areas I need to research. With my diplomacy that high (and another +60% now if your Krynn populists) I trade for every infrastructure and military tech, so I never fall behind. Sure, the AI will get hung up and never trade a few techs - basic logistics, advanced hulls and planetary invasion come to mind. But who cares if you don't get advanced hulls when it will happily trade you medium hulls? The techs it won't trade will only take you a few turns once your diplomacy research is done. A high diplomacy helps keep everyone happy with you as well. Also, dovetailing with point one, the improved governments (and trade) keep the cash flowing in.
Usually I wait until I research trade, and then "trade" trade to other civilizations to get other techs from them. From there on out I just trade techs between civilizations and hold onto all of my diplo techs. The only tech I ever research myself that I give away are the three levels of trade tech. All you need is your foot in the door to get a few techs to start your tech trading empire.

Third - Spin Control Center. You get this from Total Majesty. I know I can't fight anyone, but while I build infrastructure it keeps the few military ships I kick out looking scary. I like to put an orbital fleet manager and omega defense system next to the spin control, usually on my manufacturing capital world. Keep this world with 11 of your meanest ships at all times.

Fourth - Hit early, hit hard. As soon as my diplomacy research is done, sometimes before it is done - I pick an empire I want to take out. Figure out what weapons they use, and build a fleet to counter. Count all of their worlds, and build enough transports to wipe out the whole civilization in one turn. You simply MUST take out at least one AI in the first year and a half or you won't have enough territory to compete with the enemy. When it is time to strike - DO NOT DECLARE WAR! Not worth getting a negative diplomacy modifier. Instead, move all of your fighters and transports next to their worlds, and put a trade embargo on them. They will "know what you are doing", and declare war on you. But, they won't attack on the turn they declare war. So, after they declare war, wipe out every world. You probably won't wipe out all their ships, but that doesn't matter, territory is more valuable than ships. (new!) whether the remaining fleets go to enemies or become pirates doesn't really make a huge difference. All that matters is # of tiles you control. Maximize your territory.

Fifth (new!) - give your treaties away to people who are mad at you, while you prepare to take care of them. Nothing like another way to increase diplomacy.

Sixth - A house cannot stand divided against itself. Don't fight on two fronts. Do what you have to do to keep yourself at war with only one civ at a time. Take em down in chunks. Pay to split alliances or start wars between AIs. Ideally, you will never be at war yourself. If you are conquering someone, you do it one turn (except vs. the Yor w/new SA). Only if you make a mistake in diplomacy and someone declares war on you should you ever be in a position to be fighting a longer war.

Seventh - Use allies. I usually like to pick one or two civilizations that are a medium distance from me (the closest ones I want to conquer) that I want to hold on to for the whole game. Use all of that research and production and military they produce to my advantage. I work to build an alliance usually with two civs and keep them around until there are just 3 civs left (besides me) to break that alliance and destroy them. If one civ starts to get too far above me in military and relations aren't going well, I pay my allies to attack it, just because war will wear down both sides. Unlike a typical war declaration, if you pay an ally to go to war with someone - you don't get the "honor your alliance and go to war" dialogue, so you can stay at peace with the threat civ while your allies get blown to bits.

No deep dark secrets there. In short, money, diplomacy, and let the AIs do most of the research and fighting for you. I'm sure there are other strategies, and sometimes I will design a custom empire to try out a different tactic. The above represents my most dependable strategy for beating the game in my experience.