If you decide to use a tiled background, make sure you choose one which doesn't have too much colour variation, or it will be difficult to find a colour for the text so that it is readable throughout.

If you want a coloured background, make sure the text colours you use are contrasting. And when I say contrasting, I'm talking about hues and shades as well as the colour itself. For example, red and blue are contrasting colours, but because they are so close together in 'darkness', red text on a blue background will tend to 'flare' and become unreadable. It's logic really, but don't use dark text on a dark background.

Personally, I really like tiled backgrounds as opposed to border backgrounds, but they can look okay too. I prefer tiles mainly because I think they're more fun, especially when it's a tiled picture. Seamless tiles look best in my opinion if they're not simply patterns, but an actual texture of some sort, like fabric, paper, wood etc. But everyone of course has their own tastes.

If you want to create your own backgrounds, there are two basic ways of doing it. Many graphics programs, like PhotoImact and PaintShopPro have built-in background creators, which can be fun. Alternatively, you can tile an image of your choice, as I have with these pages. If you choose to do this, you should be careful about the kind of image you select - don't use anything with significant colour tone differences. If you have a good image but are worried about the contrast, simply reduce the contrast using a paint program such as PhotoImpact. Reduce the colour depth too, to make the picture lighter. I think it often helps to blur an image slightly too, just to make the background less sharp and significant. of course, it's entirely up to you what you think looks best. Once you are happy with the image, try out different text colours (if it is a pale image, black will usually look best).

Some good sources for backgrounds are:
Architectural ornamentation from around the world - free cultural backgrouns in .gif format.
Aron's Graphics - offers some nice tiled backgrounds among other things.
Grafxland backgrounds - a whole list of sites with free backgrounds.