T-SQL (SS2K8) :: Get Rows And Sum In Joined Table?

I want to return all rows in table giftregistryitems with an additional column that holds the sum of column `amount` in table giftregistrypurchases for the respective item in table giftregistryitems.

What I tried, but what returns NULL for purchasedamount, where I want purchasedamount to be the sum of the `amount` for THAT item, based on giftregistrypurchases.itemid=giftregistryitems.id:

SELECT (SELECT SUM(amount) from giftregistrypurchases gps where registryid=gi.registryid AND gp.itemid=gps.itemid) as purchasedamount,*
FROM giftregistryitems gi
LEFT JOIN giftregistrypurchases gp on gp.registryid=gi.id
WHERE gi.registryid=2

How can I achieve what I need?

Here's my table definition and data:

USE [tt]
GO
/****** Object: Table [dbo].[giftregistry] Script Date: 09-05-15 11:15:18 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[giftregistry](
[id] [int] IDENTITY(1,1) NOT NULL,

[code]....

Desired results:

purchasedamountidregistryidtitleogimgdescriptionURLamountpricecreatedate

[URL]