I have the Creative GigaWorks T3 and they are AMAZING, im just wondering if a Sound Card will improve the sound quality for games and music etc and if so which one would you recommend, im planning on getting the new AMD zambezi chip with an AM3+ motherboard so wondering if a sound card would be necessary.
There is a considerable difference between on board sound and a high quality sound card. The problem is that you need a set of speakers/headphones that can take advantage of the cleaner sound production of a discrete card. Unfortunately I don't know how good the GigaWorks T3 are so you may need to do some research on that subject. You also need high bit rate, non compressed source sound such as .flac and 320kbps mp3. I'm a fan of the Asus Xonar sound cards and have recently purchased the Xonar Essence STX. Make sure to read specifications and reviews on various sound cards as they are not all created equal. For example, i bought the STX because it has a high quality on-board amp for my headphones and is PCI-e x1 compatible.
The Asus Xonar Essence STX is actually a headphone/headset soundcard, with internal amplifier and those things. As gamerk316 mentioned, the HT Omega Striker and the Asus D1/DX are both extremely well-built and high quality cards, and defninitely worth the money. I wouldn't go over $100 for a soundcard without a very good sound system though (and no, a ~$1000 sound system isn't a ver good sound system). Only with a home entertainment PC would I start looking at things like the Auzentech Meridian 2G or the Asus Xonar HDAV1.3 Deluxe, which are both quite nice cards.
Though, for standard to medium-class gaming and personal entertainment, you won't get much difference from using the onboard sound on your motherboard, specially not from the new ones. The past 2~3 years or so almost all motherboards came out standard with 7.1 HD audio anyways, so you've got all you need at better quality most basic sound systems (like the Logitech Z506) can reproduce. Rather spent the extra cash on a better GPU, CPU cooler, extra RAM, wicked Blu-Ray drive, etc. etc.