The HTC Wildfire has landed but except if you have a grudge against the HTC Desire, we'd suggest that you buy the latter rather than choosing the former as the price difference is likely to be significantly less than you'd expect.
The best HTC Desire deals are still the ones from T-Mobile and Vodafone; the former gives you 600 minutes, 500 texts and 3GB mobile data while the other bundles 300 minutes, unlimited texts and 500MB mobile data.
In both cases, the contracts last two years, a free 4GB card, come with 90 days free insurance and cost only £25 per month. A shorter 18 months contract will cost the same but offer only 300 minutes and 300 texts (with mobile data), again on T-Mobile.
T-Mobile has already confirmed that it will be selling the Wildfire on a 24 month contract for as much as £20 per month which is within £5 of what they will charge for the HTC Desire.
As for the reasons to convince you to fork the extra fiver a month for the HTC, well top of the list has to be the screen. The Desire has a screen resolution of 800x480 compared to the ridiculously 240x320 on the Wildfire; that's five times lower.
Furthermore, the processor is a much slower, much older model which was used in the first generation Android-phone (HTC Magic) and there's less onboard memory.