I am really interested in big bang for the buck upgrades. I bought a Cannondale CAAD9 5 a few weeks back and have about 300 miles on it. I really like it and don't really need to change anything but I read on some forum around here that a good set of tires can make a night and day difference in ride comfort.

Is this true?

tires (and riders) are all over the place. What came on your bike?

Vittoria Zaffiro Pro Slick, 700 x 23c, foldable

and I am 225 -230 depending on the weekend.

Bontrager Race Lite Hardcase in the back. Maxxis Dentonator in the front. It's because they came on the bike I bought and they are decent tires.

Before that I had some Hutchison Equinox tires that were red. They kind of matched my CAAD9, which had some red on it.

I also bought some Forte GT2 Road Tires. They're cheap and decent for my commuter bike.

Continental Gatorskins 700X23. My old tires needed to be replaced and I wanted something w/decent flat protection. Next time I'll spring for some conti gp4000s (I started racing )

Michelin Pro 3 700 x 23c. I ride them because they come highly recommended as good tires.

gp4000 because bike forums told me to.

P2R... because I bought spares 2 years ago and I don't weight much...
I still have 2 unused spares left over.

Conti GP4000s because they are durable and worth the price.

Vittoria Ultra Speed 700 x 20 - front
Panaracer StradiusPro 700 x 23 - rear

because i still have some stock from a bulk buy sometime ago. these tires are fast.

this

Michelin Krylions. The quality seems to have improved as of late.

Gatorskins on the front, Hutchinson Intensive, both 700x23.
Gatorskins because I've heard good things about them and I got it from a trade; the Hutchinson Intensive because it was on sale for only 20 dollars so I thought I'd give them a shot. So far, they've been really good to me.

Conti GP4000s because I like them.

Michelin Orium 23s. They are inexpensive, wear well, roll well, and Michelin has always treated me well. Forte tires for the commuter.

Serfas Seca RS. Cheap, durable, and they do just fine.

Panaracer Closer 700x25 f&r 'cause I got them for a good price on Ebay and I am a big guy.

Michelin PR3, although I won't be buying more :-P The tires are great but wear fast, I put just over 2,000 on them and the rear is almost on the cords (and I weight 125...). Before that I has a Serfa Seca 2 on the rear, that tire lasted damn near forever...put like 3,000 on it and it still had lots of tread left. I think I'll be running a Continental 2000 after the PR3 gets replaced; expensive tires for training = $$$ spent.

Michelin PR2. Why, because I wanted to change from Kryliums and I found a new set of PR2's for $40.

Conti GP 4k's are great. YMMV. I just put on a 25 rear (vs. 23 up front) cause I ride a lot of crappy surfaces. I have Sp. Armadillos on my MTB. Three years, one NAIL puncture. Could have ridden it for many miles with the nail embedded, I but made the mistake of removing it 10 miles from home. Instant flat. It was doing fine til then. I got some unpleasant pinch flats with Conti Gatorskins in less than 30 miles. Maybe it was the rim's fault. (My fault mounting? Maybe, but it never happened before or afterwards with Vittorias, Specs, Conti 4ks, Panaracers.)

Anyway the 4ks are very nice puncture-resistant very good handling tires.

Hutchinson Fusion 2 Kevlar - they roll fast and don't get sliced and diced easily.

one pair of bontrager race lights, one pair of conti 3000, two pairs of cst ultra speed with kevlar. The bontragers were almost $40.00 apiece, thecontis were about $25.00 close outs, the cst's were $38.00 for the pair shipped.

Vredestein Fortezza TriComp SLick

My new favourite tyre.

Same here. They ride nice, but I really don't find them to be any "faster" than the (always on sale at PB) Hutchinson Fusion's they replaced. They do however seem to stick like glue (while making lots-o noise) in corners .

GP4000 (with the black chili compound, of course), 25mm...because they are AWESOME (and they have something called "black chili compound")!