Hi Tim,
I did notice a few things on reviewing your site, I've tried to group them in sections but inevitably there's some crossover, so bear with me!
Page Layout
The page design starts centre-aligned for the banner and main menu links, then the rest of the page seems to go askew. This pattern occurs throughout the site. On entering the portfolio page, we see four sublinks which are not aligned in any way. This seems a little careless, and will convey a poor impression to potential customers.
Site Links
Your links are not consistently displayed, therefore their behaviour is not predictable. This can seriously put off some visitors. For instance, in the gallery section they are underlined, without any hover attribute. On the services page there is a block of body text which triggers a hand cursor (in IE), but this isn't actually linked to any further content. You might want to check the 'title' selector in your stylesheet for that one!
There are even some broken or missing links eg.the 'free quote' link on the following page
www.timrendle.com/pages/web_management.html is highlighted in red (to grab our attention) but it doesn't link to 'theplan.html' which is where the details can actually be found.
Links opening new windows are not good news either.. I don't really see why your Shameless Publicity (links section) on the playground page spawns a new window? Surely this is all part of your internal site, isn't it??
Summary
There are good things about the site, don't get me wrong... I think the graphics are pretty strong, and the overall color pallette is sensibly restricted.. it's just that these could be overshadowed by some easily rectified problems.
Hope this helps in some way
Paul